Transcript
WHITE PAPER: BUSINESS BENEFITS
The Dynamic Disk Advantage Comparing Dynamic Disks to Basic Disks Jeffrey Armorer, Technical Product Manager Storage & Availability Management Group
Symantec Technical Network White Paper
White Paper: Symantec Business Benefits
The Dynamic Disk Advantage Comparing Dynamic Disks to Basic Disks Content Introduction ...................................................................................................................................... 4 Disk types ......................................................................................................................................... 4 Basic disks ........................................................................................................................................ 4 Partitions .......................................................................................................................................... 5 Dynamic disks ................................................................................................................................... 5 Advantages of dynamic disks ........................................................................................................... 7 Veritas Storage Foundation for Windows ......................................................................................... 7 Dynamic Volumes ............................................................................................................................. 8 Dynamic Disk Groups........................................................................................................................ 8 Cluster Dynamic Disk Groups ........................................................................................................... 8 Private Dynamic Disk Groups ........................................................................................................... 9 Windows Disk Management Compatible Dynamic Disk Groups ....................................................... 9 Management, Performance and Availability .................................................................................. 11 Capacity Monitoring ....................................................................................................................... 11 Automatic Volume Growth.............................................................................................................. 11 Thin Discovery and Reclamation .................................................................................................... 11 Event Notification ........................................................................................................................... 12 Subdisk Operations ........................................................................................................................ 12 Dirty Region and RAID-5 Logging ................................................................................................... 12 Dynamic MultiPathing (DMP) ......................................................................................................... 12 FlashSnap ....................................................................................................................................... 13 VxCache .......................................................................................................................................... 13 Configuration Backup ..................................................................................................................... 13 Track Aligned Volumes ................................................................................................................... 13 Volume Shrink ................................................................................................................................ 14 Volume Shred ................................................................................................................................. 14 Smartmove ..................................................................................................................................... 14 Comparing SFW to LDM .................................................................................................................. 15
Dynamically Managing Storage ...................................................................................................... 17 Migration ........................................................................................................................................ 17 Campus Clusters ............................................................................................................................. 19 Reclaiming Storage ......................................................................................................................... 21 Conclusion ...................................................................................................................................... 23
Symantec Technical Network White Paper
Dynamic Disk Advantages
Introduction When Microsoft introduced the Windows 2000 operating system, they introduced a new way of managing disks and the capacity they contained. Developed in conjunction with VERITAS Software, Windows Disk Management uses the concept of dynamic disks to allow users to dynamically configure their storage i.e. without reboots. The default disk type, referred to as basic, allows for the creation of partitions and logical drives, much in the same vein as Disk Administrator in Windows NT. Dynamic volumes are created on dynamic disks and provide the means to configure RAID and to add space. Storage Foundation for Windows provides advanced volume management and a host of other features above and beyond those natively available in Windows, and can either coexists with Windows Disk Management or displace it. The choice to coexist with or displace Disk Management can be made during installation of Storage Foundation or any time after that.
Disk types Windows recognizes two disk types – basic disks and dynamic disks.
Basic disks Basic disks are supported by all versions of Windows, and can contain primary partitions, extended partitions and logical drives. With Windows NT, basic volumes which include volume sets, stripe sets, mirror sets and stripe sets with parity could also be created. These volumes are still recognized by the Logical Disk Manager (LDM) included in Windows 2000 and later, but cannot be managed by it. In LDM, they are referred to as spanned, striped, mirrored and RAID-5 volumes respectively. Storage configuration changes done via the Disk Administrator are stored in the Windows Registry, and often require a restart of the operating system to take effect. The Registry should be backed up and Emergency Repair Disks recreated each time configuration changes are done in Disk Administrator. To extend basic partitions or repair a basic RAID set, the volumes have to be taken offline, and the operating system may have to be restarted.
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Dynamic Disk Advantages
Partitions To use a disk, it has to be partitioned i.e. divided into logical spaces. In Windows, partition types include primary partitions, extended partitions and logical partitions. A primary partition can contain only one logical drive, and is the partition type that Windows boots from. The partition that is booted from has to be designated as active. Due to the way the Master Boot Record (MBR) is structured, Windows allows up to a maximum four partitions to be placed on a hard disk. Extended partitions allow this limitation to be exceeded by allowing the creation of another partition type called a logical partition. An extended partition can be considered to be a container for logical partitions. It can be subdivided into logical partitions, each of which can each be assigned a drive letter to create logical drives. The extended partition cannot itself be assigned a drive letter, but there are no limits on the number of logical drives that can be created. In Figure 1. drives C:, D: and E: are on primary partitions. Drives F:, G:, H:, T: and Z: are logical partitions which are part of an extended partition. Logical Partitions
C:\
Primary Partition
D:\
Primary Partition
E:\
F:\
Primary Partition
G:\
H:\
T:\
Extended Partition`
Figure 1. Primary and Extended Partitions
Dynamic disks Starting with Windows 2000, dynamic storage is the supported method for managing disks and the space they contain. A disk initialized for dynamic storage is called a dynamic disk. It can hold simple volumes, spanned volumes, mirrored volumes, striped volumes, and RAID-5 volumes. With dynamic storage, you can perform disk and volume management operations without having to restart the operating system.
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Z:\
Dynamic Disk Advantages
Unlike basic disks which use the master boot record (MBR) partition table to store primary and logical disk partitioning information, dynamic disks use a 1 MB private region on the disk to maintain a database which contains information on volume types, offsets, memberships, and drive letters of each volume. The database is also replicated to each dynamic disk so that each one contains not only its own configuration information, but the configuration information for all 1
other dynamic disks in the disk group , making them more reliable and recoverable than basic disks. Free Space
Volumes
F:\
G:\
MBR
Public Region
Private Region
Figure 2. Dynamic Disk Layout
Figure 2 shows a dynamic disk layout. The MBR is still located at the beginning of the disk. At the end of the disk is the reserved private region which stores the disk’s configuration information. The rest of the space on the disk (between the MBR and the Private Region) is referred to as the Public Region, from which volumes can be created. Volumes can be thought of as the dynamic disk equivalent of the basic disk’s primary partition and, like partitions, can be formatted with a file system and mounted.
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Disk groups were introduced in Windows 2000 to identify groupings of disks that are either basic or dynamic. Basic disks reside in the Basic Group and dynamic disks in the Dynamic Group.
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Dynamic Disk Advantages
Advantages of dynamic disks Dynamic disk store their configuration information on the disks, allowing for persistence through system and OS updates. Connecting them to another host in the event of a disaster will allow Windows to access them and the data they contain. Basic disks store their configuration information in the Windows registry. In the event of a loss of the operating system, recovery has to be done from tape backup. Storage Foundation for Windows also supports automatic track alignment for dynamic volumes are created with it.
Windows Clustering Microsoft Cluster Server (MSCS) in Windows Server 2000 and 2003 and Failover Clustering in Windows Server 2008 do not natively support dynamic disks. The resource type available for disks in Windows clustering, the physical disk resource, only recognizes basic disks. Microsoft Cluster Server (MSCS) in Windows Server 2000 and 2003 and Failover Clustering in Windows Server 2008 do not natively support dynamic disks. The resource type available for disks in Windows clustering, the physical disk resource, only recognizes basic disks.
Veritas Storage Foundation for Windows The advantages of dynamic disks that are realized in the operating system are just the tip of the iceberg. With Storage Foundation for Windows (SFW), Symantec extends the OS’s capabilities through more advanced versions of dynamic disks. In addition to the volume types available with Windows Disk Management / Logical Disk Manager (LDM), SFW allows mirrored-striped volumes (RAID 0+1) to be created for a combination of high performance and fault tolerance. Mirrored 2
volumes can be created with up to 32 plexes , versus two in LDM and the Cluster Option for Microsoft Cluster Server adds a cluster resource that allows dynamic disks to be used in a Microsoft cluster. While LDM only supports a single dynamic disk group, SFW provides support for multiple disk groups, providing increased granularity and flexibility.
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A plex represents an instance of a volume. Mirrors can have multiple plexes (up to 32), while all other volume types have a single plex only.
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Dynamic Disk Advantages
Dynamic Disk Groups Windows Disk Management allows only a single dynamic disk group. If one disk has to be taken offline, all disks and volumes in the dynamic disk group have to be taken offline. Storage Foundation for Windows supports multiple dynamic disk groups. The primary dynamic disk group is reserved for Windows Disk Management compatible dynamic disks to contain the system/boot or other system critical volumes. Other dynamic disk groups will be designated as secondary. dynamic disk groups, which can be regular (SFW) dynamic disk groups, Cluster Dynamic Disk Groups, Private Dynamic Disk Groups or Windows Disk Management Compatible Dynamic Disk Groups.
Primary Disk Group The Primary disk group is reserved for the system/boot disk. If it is upgraded to dynamic, the system/boot disk will be placed in the primary dynamic disk group. As it is Windows Disk Management compatible, a system will still be able to boot from a system disk if SFW is removed. Other disks can also be placed in the primary disk group, but they will all be Windows Disk Management compatible only and, hence, limited in functionality.
Cluster Dynamic Disk Groups Cluster Dynamic Disk Groups are available with the Cluster Option for Microsoft Cluster Server (MSCS) to provide support for dynamic disks in a cluster. With its support for multiple dynamic disk groups, Storage Foundation allows multiple storage resources to be created for different applications so that when one application fails over in a cluster, other applications in separate cluster dynamic disk groups aren’t impacted. Cluster dynamic disk groups protect against multinode access when shared storage is used by the cluster. Windows Server 2008 Failover clustering requires the use of SCSI-3 compliant storage. Storage Foundation also provides support for SCSI2 storage in a Failover cluster configuration, allowing users with older storage to utilize Windows Server 2008 clustering.
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Dynamic Disk Advantages
Private Dynamic Disk Groups Private dynamic disk groups allow storage to be safely shared between systems by allowing the it to be partitioned and exclusively assigned to a specific system. As with cluster dynamic disk groups, private disk groups use SCSI reservations to protect ownership. Unlike cluster dynamic disk groups, which depend on a cluster to bring them online, private dynamic disk groups are auto-imported on system start. In non-cluster configurations where disks are shared between systems, such as for off-host operations like backups, private disk group protection should be used to protect against accidental (or malicious) importation of the same disk group on multiple hosts, which can lead to data corruption.
Windows Disk Management Compatible Disk Groups While Windows supports dynamic disks, it does not recognize the advanced version of dynamic disk group that can be created with Storage Foundation. Windows Disk Management compatible disk groups are the same version of disk group that can be created with Windows Disk Management, making them the disk group of choice when data has to remain accessible in the event that Storage Foundation is removed from the system. To ensure that the system will always be able to boot, the disk(s) containing the system and boot partitions can only be upgraded to this type of dynamic disk group.
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Dynamic Disk Advantages
Dynamic Volumes Simple Volumes – Similar to LDM, simple volumes created with SFW occupy a single disk. Additionally, SFW allows simple volumes to be dynamically relayed out as striped volumes. Spanned Volumes – With LDM volumes can span up to 32 disks, versus 256 disks with SFW. While they can be extended in LDM, they cannot be mirrored. SFW allows spanned volumes to be extended and mirrored, and allows them to be dynamically relayed out as striped volumes. Mirrored Volumes – LDM can mirror volumes up to two plexes, but cannot extend mirrored volumes. SFW can mirror up to 32 plexes, supports extending those volumes and designating a preferred read plex. Mirrors can also be created selectively across enclosures, ports, channels or targets. Striped Volumes – SFW supports mirroring, extending and dynamic relayout of striped volumes. RAID-5 Volumes – Cannot be mirrored or extended with LDM. SFW also does not support mirroring of RAID-5 volumes, but can extend them. Mirrored-Striped Volumes (RAID 0+1) – Supported with SFW only. Mirror-striped volumes can be extended. Table 1 Dynamic Volume Types Volume Type
LDM Features
SFW Features
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Comments
Dynamic Disk Advantages
Management, Performance and Availability Dynamic disks created with Storage Foundation for Windows provide features that enhance storage management, improve performance and increase availability. Some of these features include:
Capacity Monitoring The capacity of dynamic volumes is monitored so that when preset thresholds are reached, an action is taken based on the policies set for the volume. Actions include logging an alert and/or sending an e-mail or automatically growing the volume. Capacity Monitoring is cluster aware; settings made on one node in a cluster are replicated to the other cluster nodes.
Automatic Volume Growth Can be set on individual volumes so that they automatically grow when the amount of space used reaches a preset, user defined threshold. Policies can be set for the size by which the volume should grow and for either unrestricted growth i.e. no maximum size limit set for the volume, or restricted growth where the volume grows by the specified amount, but never exceeds the maximum specified size. Automatic volume growth can also be used with thin provisioned storage to trigger LUN expansion, thereby overcoming limitations imposed by the Windows file system in those environments. Ntfs’ tendance to wander over a volume can cause unnecessary allocation of storage in the array. Creating a small volume will limit NTFS wandering on the disk. Enabling automatic volume growth will cause the volume to grow automatically when the critical threshold is reached, triggering allocation in the array.
Thin Discovery and Reclamation Storage Foundation provides a framework for discovery of thin provisioned storage and, for supported arrays, reclamation of free space that was previously allocated. Storage that is provisioned thinly will cause allocation in the array as file system usage on a volume increases. When space has been allocated in the array, it will remain allocated even if space is later freed up on the volume. With its thin provisioning framework, Storage Foundation not only discovers thinly provisioned storage but, for supported arrays, provides a mechanism to reclaim space that has been freed up. Reclamation can be done at the volume level, the disk group level or both, and can be manual or scheduled.
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Dynamic Disk Advantages
Thinly provisioned LUNs that are discovered by SFW are displayed in the Veritas Enterprise Administrator as either disks with a green sector that has an asterisk if they support thin reclamation, or as disks with a red sector if they don’t. Use Storage Foundation to reclaim free space from dynamic volumes and dynamic disks which have been thinly provisioned.
Event Notification Notifications can be configured to be sent via SMTP e-mail, pager or SNMP traps after certain events occur.
Subdisk Operations Subdisks identify the disk location and size of each contiguous disk area in a volume, and are the basic units by which Storage Foundation for Windows allocates disk space. Move Subdisk, Split Subdisk and Join Subdisk commands are available so that subdisks can be moved to other locations within a dynamic disk group, or they can be split and joined back together. These commands would be used for storage load balancing e.g. moving a subdisk from a disk that is experiencing high I/O to another less busy disk in the disk group, disk failure or removal, or disk phase-out.
Dirty Region and RAID-5 Logging Dirty Region Logging (DRL) uses a log-based recovery method to quickly resynchronize a mirrored volume following a system crash. Without DRL, mirrors would have to be fully resynchronized i.e. the full contents of the volume must be copied between the mirrors of the volume. RAID-5 Logging is used to quickly reactivate a RAID-5 volume following a system crash. Without it reactivation of the entire volume is necessary, which can take a very long time.
Dynamic MultiPathing (DMP) Available as a licensed option, DMP allows the use of multiple paths between a host and its storage subsystem to provide storage fault-tolerance and load balancing. The Dynamic MultiPathing option supports Microsoft’s MPIO framework through MPIO DSMs (Device Specific Modules), which provide for multiple load-balancing policies and support for ALUA (Asymmetric Logical Unit Access) , which enables active/active load-balancing for Active/Passive Concurrent and Active/Active Asymmetric arrays. Storage Foundation management packs for Microsoft Operations Manager and System Center Operations Manager provide an interface through which DMP path performance statistics and graphing are made available.
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Dynamic Disk Advantages
FlashSnap Create independently addressable snapshot volumes that are point-in-time copies of data volumes, which can be used for quickly recovering from a disaster or for offhost operations. FlashSnap is integrated with Microsoft’s Volume Shadow Copy Service (VSS) to allow for consistent snapshots of Microsoft Exchange Server 2003 and 2007 Storage Groups, Microsoft SQL Server 2005 and 2007 databases, SharePoint Server 2007 databases, components across farms or entire farms, and Enterprise Vault 8.0. VSS guarantees the integrity of snapshots created via its framework. FlashSnap also integrates with Microsoft SQL Virtual Device Interface (VDI) through the vxsnapsql command line utility. Snapshots can be scheduled via the VSS Snapshot Wizard or , for Microsoft Echange and SQL Server, via the Quick Recovery Configuration Wizard, which is available in the Solutions Configuration Center.
VxCache Allows a cache memory pool of up to 4 GB to be designated for use by specific volumes on which VxCache has been enabled to improve read performance of those volumes. VxCache should be enabled on read intensive volumes only.
Configuration Backup Storage Foundation for Windows provides GUI and CLI utilities for backing up the dynamic disk configuration. Automatic configuration backups can be configured to occur at preset intervals via the Control Panel Configuration Backup utility. Dynamic disk group configurations can also be backed up manually from the GUI or via the command line utility, vxcbr.
Track Aligned Volumes Dynamic volumes created with Storage Foundation for Windows can be automatically aligned to store data within the boundaries of the physical tracks of the hard disk with the Track Alignment feature, taking into account the different alignment offset requirements for different hardware vendors. Storing data in this way helps optimize I/O performance. This provides a non-invasive method of aligning volumes, making it easier for users who previously depended on the invasive procedure accomplished with the Microsoft Diskpart utility.
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Dynamic Disk Advantages
Volume Shrink Dynamic volumes that are either RAW or NTFS formatted can be decreased in size with the Shrink Volume command. Data remains intact. SFW’s volume shrink operations maintain 15% free space on volumes for defragmentation per Microsoft recommendation.
Volume Shred Storage Foundation for Windows also includes the Shred Volume feature. Shredding a volume completely removes all data from the volume and deletes it. The volume is completely overwritten and then removed. All data is completely lost. The volume shred feature meets Department of Defence 3-pass and 7-pass overwrite compliance requirements.
SmartMove Storage Foundation for Windows includes the SmartMove feature, which enhances the performance of mirror operations and subdisk moves by reducing the time required for resynchronization for these operations. Smartmove is supported with NTFS volumes, and uses the NTFS metadata to resynchronize only selected regions of the volume.
Recommendations & Best Practices When using DRL or RAID-5 logging, move the log volume to a disk other than one hosting the data volume to
improve performance Create separate dynamic disk groups for different applications or application components e.g. Exchange Storage
Groups; SQL databases Use Private Disk Groups when sharing storage between systems outside of a cluster. After resizing a volume, delete and re-add log volumes (DCO, DRL, RAID-5 Logging) to optimize performance. Designate a preferred read plex when mirroring across geographic distances or when mirroring to lower tier disks. Backup the dynamic disk configuration regularly. SFW can be configured to automatically backup the dynamic
configuration at preset intervals with the Configuration Backup utility in Control Panel. Use Online Monitoring to hot spots and the Move Subdisk feature to move subdisks around to balance load and
optimize storage performance. Use the Dynamic Relayout feature to change the attributes of a striped volume (stripe unit size; number of columns)
or to change a concatenated volume to a striped volume. For snapshots, move the log volume (DCO) from the disk containing the data volume to another disk to improve
performance.
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Dynamic Disk Advantages
Comparing SFW to LDM The following table compares the features currently available in Storage Foundation 5.1 SP1 for Windows with those available in Windows Server 2003 Logical Disk Manager (LDM) and Windows Server 2008 Disk Management.. Table 2 Feature Comparison Feature Comparison
W2K3 LDM
W2K8 LDM
SFW
x
x
System/Boot Disk Encapsulation
x
x
x
x
x
Fault Tolerant Volumes
x
x
x
SFW
W2K8 LDM
Feature Comparison
W2K3 LDM
Veritas Storage Foundation 5.1 SP1 for Windows (SFW) : Windows Server Logical Disk Manager (LDM)
Storage Management Storage Management & Reporting
Feature Comparison Availability
x
Domain-Wide Storage Management GUI Command Line Interface (CLI)
x
x
x
Mirrored Volumes (RAID-1)
x
x
x
Heterogeneous Storage Management
x
x
x
RAID-5 Volumes
x
x
x
Drag-n-Drop Storage Management
x
Mirrored-Striped Volumes (RAID 0+1)
N/A
N/A
x
Storage Event Log
x
Automatic Volume Growth
x
x
Storage Availability
x
Volume Shrink
x
Volume Shred
x
Disk Replacement
x
SmartMove
x
Disk Evacuation
x
Volume Growth
Striped Volumes
x
Hot Relocation Mirror across Enclosures (Port, Channel, Target) Configuration Backup
Mirrored Volumes (RAID 1)
x
Multi-pathing
x
Heterogeneous Array Support
x
Simple & Spanned Volumes
x
x
RAID-5 Volumes
x
x x
x x
x
x
Path Failover Protection & Load Balancing
x
x
x
ALUA Support
x
x
SNMP Framework Support
x
SCSI-3 PGR Support
x
x
S.M.A.R.T. Disk Monitoring
x
Snapshots
Capacity Monitoring
x
VSS Support
x
x
x
Paging/Email
x
x
x
x
Mirrored Striped Volumes (RAID 0+1) Proactive Storage Resource Monitoring
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N/A
N/A
VSS Snapshot Provider
x
Dynamic Disk Advantages
Feature Comparison
SFW
x
x
x
x
x
x
x
x
x
x
x
x
Feature Comparison
W2K3 LDM
W2K8 LDM
Enterprise Wide Storage visibility and Mgmt. Storage Analysis & Reporting
SFW
Storage Management Custom Monitoring Settings
W2K8 LDM
Feature Comparison
W2K3 LDM
Veritas Storage Foundation 5.1 SP1 for Windows (SFW) : Windows Server Logical Disk Manager (LDM)
Snapshots x
x
Dynamic Disk Support Disk Group Support
x x
x
x
x
x
x (disks)
x
x (1)
x
x
x
x
x
x
x
x 32 plexes
x
2
x 2 plexes
x
x
x x
x
x
x
x
x
x
x
Clustering
Performance
x x
x
x
x
x
x
x x
x HA/DR
x x
x
x x
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x
x
x
x
x
x
x
x
x x
x
x
Maintenance x x
x
Thin Provisioning x x
Dynamic Disk Advantages
Dynamically Managing Storage Now that we’ve seen the many features and advantages that dynamic disks bring to the table, let’s look at how Storage Foundation for Windows can be used to practically address real world scenarios in the data center.
Migration Data centers today are more and more challenged by the need to optimize and economize, which means that they have to find ways to capitalize on current assets. Repurposing older storage; moving the most critical data to more expensive storage, and less critical data to less expensive storage. Moving data from one storage array to another, especially a different type of array, can be costly, both in terms of time and resources. Hardware replication can be used, but this requires the use of identical arrays and proprietary software which can be very expensive. The data can be backed up and restored to the new array but, again, very expensive in terms of down time. A third and more economical option would be to use some sort of host based application that doesn’t care about the storage underneath and that can move the data while keeping the data available and applications online. Storage Foundation for Windows is such an application. Running on a host, SFW sees all connected storage as a virtual pool, allowing data to be freely moved between disks, LUNs and arrays, while keeping it online and accessible. The simple process involves dragging a volume from its current disk location to disk in another storage subsystem that’s seen by the host. The operation involves mirroring of the volume to the new location and removing the original plex after resynchronization completes. The SmartMove feature helps reduce the time taken to complete the operation by causing only the used blocks on the volume to be resynchronized. If migrating to thin provisioned storage, the operation will cause only the amount of space necessary to host the volume’s data to be allocation in the array.
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Dynamic Disk Advantages
Figure 3. Migrating Data
In Figure 3 above, SFW running on the server sees all storage; internal, DAS and SAN, as local to the server. With its ability to dynamically move data between attached disks via the Move Subdisk feature, SFW allows for simple migration of the volumes and data on the internal disks and the direct attached array to the higher capacity, higher performing SAN attached array. Users can continue to access their data and applications throughout the process. This operation can only be done on SFW dynamic disks.
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Dynamic Disk Advantages
Campus Clusters While clustering an application protects it against failures at the hardware level, more wide ranging failures, such as a power failure that impacts the entire datacenter, can still lead to the application becoming unavailable. This can be countered by stretching the cluster so that it leverages another datacenter and hardrare resources there. Campus clustering extends application availability beyond the confines of a single datacenter to span two datacenters by leveraging servers and storage subsystems located at each, and the fiber channel connections between them. Data has to be shared between the sites. Replicating the data between the sites via the hardware can make the data available at both data centers, but this can be cost prohibitive and reduce flexibility, as hardware replication solutions typically require identical storage at both ends. In environments where different types of storage are used, this can become a very complex and expensive undertaking. Hardware has to be duplicated at both sites and management becomes difficult as different applications have to be used for the different hardware solutions. Mirroring the data between the arrays at each site without them having to be identical would help reduce complexity and increase flexibility. Having a single, common management interface would also improve efficiency by reducing the number of applications that would be required if different types of hardware are used. Storage Foundation runs on the host, allowing for the virtualization of all storage attached to that host. LUNs presented from different arrays can be placed in a single dynamic disk group and mirrored volumes can be created using any of the disks in that disk group. Arrays can be located across distances supported by a Fiber Channel, and volumes can be mirrored across disks from each array. With its support for dynamic disks in a cluster (Veritas Cluster Server, or Microsoft’s MSCS or Failover Cluster), Storage Foundation facilitates the stretching of clusters across metropolitan distances so that separate sites can be created in a single Campus Cluster. Mirrors can be designated across enclosures to ensure that volume growth occurs correctly at each location in the cluster.
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Dynamic Disk Advantages
Site A
Site B
Cluster Node 1 + SFW
Cluster Node 2 + SFW
Switch
Switch
Array 2 Array 1
Mirrored Volume
Figure 4. Campus Cluster
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Dynamic Disk Advantages
Reclaiming Storage Imagine suddenly having to deploy a new database that requires dedicated space, but there are no available disks large enough to host it. A request to the Storage Administrator to allocate new storage requires a lengthy process to fulfill. While collectively, the required amount of space may be available across currently available storage, the fact that it’s spread out among various disks and arrays will not satisfy the requirement for dedicated, consolidated space. Having a way to easily reclaim and consolidate the fragmented space would not only save time, but also improve the bottom line by more optimally utilizing existing capacity. Storage Foundation for Windows, with its ability to manipulate volumes via moving, splitting and joining subdisks, makes this possible. In the following scenario, storage is reclaimed by splitting volumes and moving the subdisks to other locations.
Vol 1 Vol 2
Vol 3
Vol 4 Figure 5. Disks with volumes and free space
In Figure 5 above, the three disks each contain volumes and some free space.
Vol 1 Vol 2 Vol 4
Vol 4
Subdisk 1
Subdisk 2
Vol 3
Figure 6. Splitting a volume
By using the Split Subdisk feature available in SFW, Vol 4 is split into two subdisks, Vol4Subdisk 1 and Vol4-Subdisk 2, as shown in Figure 6.
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Dynamic Disk Advantages
Vol 4
Vol 1 After Vol 2
Subdisk 1
Vol 3 Vol 4 Subdisk 2
Figure 7. Moving Subdisks
In Figure 7, the Move Subdisk feature is used to move those subdisks to the free space on the other two disks by dragging and dropping them there; the volume remains online and accessible during the operation.
Vol 4
Vol 1 Vol 2
Subdisk 1
Vol 3
Vol 4 Subdisk 2
Figure 8. Storage reclaimed
The disk that originally contained Vol 4 becomes free to host another volume (Figure 8).
Vol 1 Vol 2
Vol 3
Vol 4 Figure 9. Move and Join Subdisks
When additional storage is available, Vol4-Subdisk 1 and Vol4-Subdisk 2 can be moved to a new disk and re-joined using the Join Subdisk feature (Figure 9).
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Dynamic Disk Advantages
Conclusion In their article “Solution Spotlight: Dynamic Volume Management” Microsoft says “One of the major improvements provided by Windows 2000 is the operating system's dynamic volume management utility…” Dynamic disks offer many critical advantages over basic disks and, with Storage Foundation for Windows, extend those advantages beyond what’s available the operating system, opening the door to several more possibilities for dynamically managing storage, reducing both planned and unplanned down time, and optimizing utilization and performance.
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