Midrange SANs with high-end features from Compellent, Xiotech

Next, if you have the optional Data Progression software installed, data is migrated from the highest-performance tier to the lowest during a period of 12 days. This migration happens automatically, based on whether the data has recently been accessed and how often. Data Progression can be enabled on a per-volume basis, but it is not based on additional rules -- it’s either on or off for the whole volume and uses as many tiers of storage as are available.

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Thin provisioning allows you to create a virtual volume as large as the OS will allow, of which only a small part is actual disk space. For example, the initial actual size of a 2TB virtual disk could be 10GB, but you will be able to expand that size dynamically as you wish, up to the 2TB size, without changing anything on the server. You can even resize the partition to more than 2TB, as long as the OS supports it.

Snapshots create copies of data that can then be used to recover data or make backups to tape. Snapshots use single-instance at the block level, so if you make a snapshot, change a few files, and make another snapshot, only the blocks that have been changed are rewritten. This saves huge amounts of space and speeds up the snapshot process. The default template for replays is daily, weekly, and monthly, but it’s easy to set to any frequency you like.

In addition to snapshots, you can replicate a volume in real time (synchronously), at scheduled intervals (asynchronously), and semi-synchronously -- the system doesn’t wait for acknowledgement before sending the next packet. An auto-replay feature restarts an asynchronous transfer if it’s interrupted to ensure data integrity.

Compellent offers excellent reporting tools, which show topics such as trends of space in use, progression, and migration. To upgrade other SANs, you can copy to or from external disks and Compellent storage units, although there is currently no way to designate external disks as a fourth tier. The system supports Microsoft’s VSS (Volume Shadow Copy Service) for backups of open databases and Exchange system files.

All in all, Compellent Storage Center 3.3 has all of the bells and whistles available on much more expensive systems, at an affordable price, and with excellent performance and usability to boot.

Xiotech Magnitude 3D 3000e
The Magnitude 3D 3000e system is the smallest of several systems offered by Xiotech, and it has the benefit of a clear and easy migration path that will not interrupt access to the data stored on the system.