Transcript
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Virtual Disk Library Deployment with BakBone NetVault By deploying virtual disk libraries (VDLs), IT organizations can take advantage of highspeed disk technologies for backup processes while benefiting from the portability and security of tape for long-term data retention and disaster recovery. This article explains how using BakBone NetVault™ tape backup and restore software with VDLs can help organizations make effective use of tape media, achieve quick recovery, and back up data within short backup windows. BY JET MARTIN
V
irtual disk libraries (VDLs) offer an efficient media
failures. Because a VDL uses disk, there is no need to
backup paradigm for organizations that use Dell hard-
match speeds between the data source and the device. A
ware. A VDL allows administrators to emulate, or virtualize,
VDL can capture data in “drips” or “blasts,” then copy the
a tape resource (such as tape, a tape drive, or a tape library)
data to virtual media slots as a save set. These advantages,
on disk. When using VDLs, tape can become a strategic
among others offered by VDLs, can help administrators
component of an organization’s data protection strategy,
streamline the backup process.
but not the major element of the strategy. IT staff can create multiple, duplicate copies of backup jobs from the
The mechanics of VDLs
VDL to tape, or vice versa. Storing backup data on a VDL
A VDL consists of directories, called drives and slots, on a
also allows data copy jobs to be run offline to minimize
disk. These drives and slots each contain numbered direc-
impact on the network, application servers, or workstations.
tories, which are unique for each drive or slot. The media
Administrators can also set up specific backup policies such
file that resides in each numbered slot directory represents
as retention dates and media groups for VDLs.
a “tape” in the virtual library, while a media file in each
Because they are not physical entities, VDLs are
numbered drive directory represents a “drive.”
immune to the mechanical difficulties of tape backup over
BakBone’s NetVault tape backup and recovery software
a network. One example of such an issue is shoe shining—
treats VDLs as if they were physical libraries, so administra-
a scenario in which the incoming data stream to be writ-
tors do not need to manage a VDL any differently then they
ten to tape is slower than the write speed of the tape
would a physical tape library. As with a physical library,
drive. This mismatch in speed causes the tape drive to
the more drives the VDL contains, the more simultaneous
frequently stop, rewind, and then start again when the
backups can be performed. Each VDL is usually configured
next block of data arrives. Shoe shining may not only
using a minimum of eight slots, with many more slots
negatively affect the performance of the backup but may
than drives. These extra slots allow for proper handling
also cause significant wear and tear on tape media and
of backup retention cycles. In addition, different operat-
tape drives, which can lead to premature media and drive
ing systems may impose limits on the maximum file size,
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Reprinted from Dell Power Solutions, October 2004. Copyright © 2004 Dell Inc. All rights reserved.
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STORAGE
Finance
Engineering
Sales and marketing
Dell OptiPlex™ desktops
Dell Precision™ workstations
100 Mbps
100 Mbps
Dell Latitude™ notebooks
to physical tape, then define
100 Mbps
Gigabit Ethernet LAN
enough virtual tape drives to back up all the clients within the allotted hour.
Dell PowerVault 775N NAS
• Linux OS • NetVault client
Staging versus multiplexing
Dell PowerEdge 2650 Dell PowerEdge 2600
Dell PowerEdge 2600
• Windows OS • Microsoft Exchange
• Linux OS • Oracle/CRM • NetVault SmartClient • Oracle APM
Server/e-mail • NetVault client • Exchange APM
• Linux OS • NetVault backup server
Dell PowerEdge 2600
• Linux OS • MySQL/SFA • NetVault client • MySQL APM
Dell PowerEdge 2600
• Linux OS • MySQL/CAD and CAM • NetVault client • MySQL APM
Fibre Channel SAN Dell/EMC AX100 storage array
• NetVault VDL
Multiplexing is another approach for backing up multiple clients to limited tape drives within a short backup window. In multiplexing, multiple streams of backup data are sent to one
Migration to tape
Data flow
Dell PowerVault 136T tape library
tape device. This method has several drawbacks. First, a backup of any given client will
Figure 1. Enterprise IT environment
use more tape than is actually which can affect the number of slots needed for handling the data.
required. Therefore, this approach may necessitate handling more
When the NetVault VDL is configured for Dell™ PowerEdge™ servers
tapes per client backup than a nonmultiplexed approach. Because
and the number of slots and media capacity are defined, media files
mulitplexing requires more media, the probability of failure is higher.
can be created and the space can be pre-allocated in the VDL.
The time required for restoring data is also longer because more
Administrators may also install an optional Application Plugin Module
tape needs to be scanned for a given restore time, and data must
(APM) for Oracle®, MySQL, Sybase, PostgreSQL, and various other appli-
be reconstructed from multiple data streams. Multiplexing also
cations. These modules are designed to automatically add application-
heavily uses CPU resources on the backup server, because data streams
specific components to the backup and restore selection criteria
must be reorganized and packed into a multiplexed stream.
that appear on the NetVault graphical user interface (GUI). From
Although the VDL staging approach requires disk space for
this common GUI, administrators can manage all backup and restore
the virtual library resource allocation, each client’s backups are
operations across a storage area network (SAN), network attached stor-
contiguous on tape, which helps to conserve media, enable fast
age (NAS), wide area network (WAN), or local area network (LAN).
restore jobs, and minimize the chance of failure.
Advantages of VDL staging
A VDL staging scenario
VDL staging can be useful in two types of situations. For example, if
The following example illustrates an enterprise backup scenario
a company has a massive file system with millions of files, a typical
using VDL staging. Acme Engineering, a fictitious company, has
server might not be able to read the files fast enough to stream data to
approximately 250 employees in several functional units: finance,
today’s high-performance tape drives. This can lead to shoe shining and
engineering, and sales and marketing. The company has worldwide
premature drive or media failures. Because shoe shining occurs only
operations, with corporate headquarters in the United States and
with tape storage, not disk storage, performance degradation that can
sales offices in Europe and Asia.
result from shoe shining is not an issue when backing up to a VDL.
The Acme IT infrastructure is configured for the following
In another instance, an organization’s backup window may be
applications: e-mail; accounting and finance; customer relationship
too small to back up several clients onto a limited number of tape
management (CRM); sales force automation (SFA); computer-aided
drives. In this case, a VDL with enough virtual drives can back
design (CAD) and computer-aided manufacturing (CAM); order
up all clients simultaneously. Performance in this situation would
entry and order processing; file and print serving; and personal
depend on network bandwidth; a Gigabit Ethernet network would
productivity (see Figure 1).
likely be required to handle a heavy backup load. For example, sup-
Network configuration. In the Acme enterprise scenario,
pose the backup window is too small for an administrator to back
the NetVault backup server is running the Red Hat® Enterprise
up five clients in one hour, each with 10 GB of data, using only
Linux® ES 3 operating system (OS) hosted on a rack-mounted Dell
one tape drive performing at 18 GB/hour. Using VDL staging, the
PowerEdge 2650 server connected to the Gigabit1 Ethernet LAN back-
administrator could first back up to multiple virtual tape drives, copy
bone. Attached to the NetVault backup server is a Dell/EMC AX100
1 This term does not connote an actual operating speed of 1 Gbps. For high-speed transmission, connection to a Gigabit Ethernet server and network infrastructure is required.
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STORAGE
storage array with 3 TB of disk capacity and a Dell PowerVault™ 136T
of shoe shining. Writing these files to disk by using VDL staging
tape library configured with three Linear Tape-Open Ultrium 2
addressed both issues.
(LTO-2) tape drives and 72 slots. The AX100 storage array is con-
A second consideration was the restore pattern for this data. The
figured within NetVault as a VDL with four drives and 15 slots for
pattern showed that nearly 80 percent of restore requests were associ-
disk-to-disk backup.
ated with data that had been backed up from the PowerVault 775N
NetVault clients are installed and configured on four Dell
NAS server. Of those restore requests, 80 percent occurred within four
PowerEdge 2600 servers and a Dell PowerVault 775N NAS server.
days of the last access of the file. Keeping at least four days of data
A NetVault SmartClient is installed on the CRM application server
on the VDL resulted in much faster restore times compared to tape,
because of the size (1.3 TB) of the underlying Oracle database. The
helping increase user productivity. The 3 TB VDL on the AX100 stor-
SmartClient allows the client to write directly to the SAN-attached
age array allowed more than a week’s worth of incremental backup
storage media (VDL and tape library). Additionally, NetVault APMs
data to be stored on disk, which further increased the likelihood that
for Microsoft® Exchange, Oracle, and MySQL are installed and
restore requests could be serviced directly from disk.
configured on the appropriate applications servers to address the requirement for hot backups of these applications—that is, backups
Consolidation of file system backups
performed while applications are up and running.
Combining a backup-to-disk approach with the NetVault Consolidated
In this example, Acme has 5 TB of data in its environment that
backup feature helps administrators create a synthetic full backup
changes an average of 10 percent (500 GB) per day. The PowerVault
without actually running a full backup each week. Initially, adminis-
775N NAS file server has 2 TB of storage containing more than
trators must run one full backup to serve as the base. Once this full
two million files. The backup window is limited to just six hours
backup has been created, all future full backups can be performed
(between 10:00 P.M. and 4:00 A.M.).
by combining the previous incremental backups kept on disk and
Enterprise backup policy. The Acme scenario uses a disk-todisk-to-tape backup strategy as follows:
the last synthetic full backup written to tape. The Consolidated backup feature can help eliminate the need to run weekly, resource-intensive full backups, which tend to consume
• • • •
Incremental backups to the VDL occur Monday through
large amounts of network and server bandwidth. In addition, con-
Friday with a seven-day retention period.
solidated backups do not consume system resources, thus allowing
Weekly full backups directly to tape occur on Saturday with
full backups to be run at any time of the day without an adverse
a four-week retention period.
effect on production operations. Although consolidated backups
Weekly full backups are duplicated; the original is rotated
consume backup server, VDL, and tape library resources, these
off-site for disaster recovery purposes.
resources are typically not needed during normal business hours.
The end-of-month full retention period is three months.
Therefore, consolidated full backups can be run during business hours, when IT staff is more likely to be available to monitor prog-
Backup policy considerations. The backup policies deployed
ress and help ensure successful backups.
in the Acme example were driven by several key considerations. The first was the limited backup window. The sheer volume
Efficient, cost-effective data protection
of data prevented Acme from conducting full nightly back-
The loss of critical business data can be damaging if not devastating
ups, which led to incremental backups Monday through Friday
to any business. BakBone’s VDL capability offers an efficient, cost-
and full backups on Saturday. The result was an average of
effective way to use disk-based technologies to enhance data pro-
500 GB backed up each night and more than 5 TB each weekend.
tection strategies. When combined with Dell hardware, BakBone’s
Based on Acme’s configuration of network bandwidth capacity, the
approach to delivering disk-to-disk backup can help enhance the
number of physical tape drives, and write speeds of the LTO-2 drive,
speed and reliability of backup and recovery operations.
Acme’s backup needs would not have dictated a disk-to-disk-to-tape data protection strategy. Nevertheless, several factors drove Acme to implement a VDL solution in which incremental backups could be written to disk and later transferred to physical tape.
Jet Martin is director of product management at BakBone Software, an international data protection solution provider that develops and distributes data backup, restore, and disaster recovery software for network storage and open systems environments worldwide.
One factor concerned the characteristics of the data being backed up on the PowerVault 775N NAS server. Because of the large number of very small files, it was difficult to keep the LTO-2 tape drives spinning. The effect was long backup times and
F OR M ORE INF ORM ATION
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