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Smaller organizations typically have lower
overall storage requirements and fewer users, so the demand for
capacity and performance are not so acute. Instead, the midsized
storage enterprise favors attributes like cost and ease. Midrange
storage arrays hold a limited number of disk drives and can be far
less expensive than large enterprise-class behemoths -- often
providing a modular footprint that can scale within the rack as
storage needs grow. Midrange arrays cover a lot of ground in
today's storage organizations. For example, a midrange array can
start with about 10 terabytes (TB) using 20 drives -- all the way
up to 500 disk systems offering 250 TB or more. But midsized
storage systems are about more than capacity and disks. They must
also be simple to deploy, configure and manage without the need for
dedicated administrators. For example, iSCSI connectivity and
wizard-driven management interfaces are easily found in midrange
storage arrays.
Although midsized companies can easily adopt a variety of
midrange storage platforms, the actual choice of an array product
demands a careful consideration of the cost, performance and
management tradeoff. Now that you've reviewed the
essential issues involved in any storage area
network (SAN) upgrade, this Buying Guide focuses on specific
considerations for midrange disk array systems. You'll also find
a series of specifications to help make on-the-spot product
comparisons between vendors, including 3PARdata, EqualLogic,
Hitachi Data Systems (HDS) and Sun Microsystems.
Consider the connectivity and disk support. Midsized
storage organizations can potentially employ a wide range of
storage architectures, so it's important to match the current
architecture with a prospective storage array. For example, the
array may need 4 Gbit Fibre Channel ports for a full-fledged SAN,
IP connectivity for an iSCSI SAN or network attached storage (NAS).
Also select a midrange storage array to accommodate the disk
type(s) needed for the intended service level. For example, Fibre
Channel disks will meet top storage performance, but generally
offer the least capacity. SATA drives offer the largest capacity,
but the lowest performance. SAS drives often rank somewhere in the
middle -- offering good nearline performance in large capacity
drives.
Evaluate RAID options. You should generally expect a
midrange storage array to support RAID features, but be sure to
determine if the RAID levels are appropriate for the disk types
that will be deployed. For Fibre Channel and SAS drives,
single-parity RAID (e.g. RAID-5) is typically adequate. SATA drives
often present reliability concerns in storage arrays, and
dual-parity RAID (e.g., RAID-6 or a proprietary RAID-DP version)
guards against the potential data loss caused by multiple drive
failures, or the loss of a second drive while a first failed drive
is rebuilding.
Consider the scalability. Chances are that you'll be
upgrading the midrange storage array at some point during its
service life. It's important to consider the cost of upgrades, the
ease with which upgrades can be performed and the level of storage
service disruption that should be expected during an upgrade
process. For example, look for a midrange array that can accept a
storage upgrade without downtime and handle the provisioning and
migration of data without disruption to current users or
applications. Beyond the scalability of sheer capacity, also
consider the scalability of performance. Investigate the
performance impact of capacity upgrades, and consider the tactics
available to overcome any performance bottlenecks.
Consider the support for management and disaster
recovery. Midrange storage arrays should be configurable and
manageable by the existing IT staff or storage administrator.
Training should be minimal -- usually included with the purchase --
and the new array should not add significantly to the total storage
management overhead. Midrange arrays should also be included in the
organization's disaster recovery plan, so consider any disaster
recovery tools, such as remote replication or remote snapshot
software, included with the system. If disaster recovery tools are
already in place, make sure that those tools will support the new
midrange array. Otherwise, the new tools may add more overhead to
the disaster recovery process.
Consider the process and impact of data migration. It's
not enough to simply buy, install and configure a storage array ---
the data from existing storage systems must often be migrated to
the new storage array. The process of data migration is often
problematic, and unforeseen issues can easily disrupt users and
mission-critical applications. This is particularly true for
smaller organizations with limited IT staff. When considering a
midrange array acquisition, take the time to sit with a vendor and
discuss migration strategies before the purchase. Understand the
process and problems involved. Develop a migration plan that the
vendor is willing to assist you with.
Consider your escape plan. Not all system upgrades or new
implementations go smoothly. When considering a midrange storage
array, it's important to include a recovery plan along with a
migration plan. If the deployment goes awry, know the steps needed
to "back out" of an installation or undo a migration so that normal
operation can be recovered quickly. In many cases, the vendor can
help to establish a sound fallback plan.
The midrange storage array product specifications page in this
chapter covers the following products:
- 3PARdata; InServ E200 Storage Server
- EMC; Centera for mid-sized enterprise
- EMC; Clariion CX3 model 20
- EqualLogic; PS3800XV
- EqualLogic; PS400E
- Hewlett-Packard ; StorageWorks 4000 Enterprise Virtual
Array
- Hewlett-Packard ; StorageWorks 6000 Enterprise Virtual
Array
- Hewlett-Packard; StorageWorks 8000 Enterprise Virtual
Array
- Hitachi Data Systems .; Adaptable Modular Storage
AMS200
- Hitachi Data Systems .; Adaptable Modular Storage
AMS500
- Hitachi Data Systems.; Thunder 9530V entry-level storage
deck
- IBM; DS4800
- IBM; DS4700 Express
- Network Appliance .; FAS3000
- Pillar Data Systems .; Axiom 500
- Sun Microsystems .; StorageTek 6920 System
- Sun Microsystems .; StorageTek 6540 Array
- Xiotech Magnitude 750-2 iSCSI Storage
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