Compellent extends tiering to SAS

Compellent is adding SAS disk tiers to its SAN and protecting against double drive failures with RAID 6.

Storage Center 5.0 is a major evolutionary release of Compellent's array software. It adds facilities to work better with virtual servers, short-cut the initiation of a replicated disaster recovery site, simplify data protection for complex applications and lift array port efficiency.

Compellent's storage area network (SAN) storage arrays automatically move data at the block level between solid state drive (SSD), Fibre Channel and SATA disk drive tiers so as not to waste expensive SSD and fast disk drive storage. It is increasing the flexibility of its storage tiers by adding full-scale SAS drive support.

There can be from six to 384 SAS drives with Fibre Channel or iSCSI server connectivity. A 12-drive 3Gbit/s SAS enclosure can have a mix of fast 15K and slower 7K, higher capacity SAS drives, so that a performance tier and capacity tier can co-exist in the same enclosure.

Bob Fine, Compellent's product marketing director, said that wholesale SAS adoption wasn't possible before because: "SAS Xyratex enclosures, SAS HBAs from LSI and SAS drives were not as robust as Fibre Channel" equivalents. The SAS capability can be added to most Compellent array controllers via a software upgrade.

Support for SAS II, running at 6Gbit/s, will be added when all the components needed are commercially available.

RAID 6 protection against a failure of two drives is being added to the slower tiers of Compellent's storage. The fast tiers use RAID 10 so that performance is less affected by RAID rebuild time following a disk failure. The slower tiers are optimised for capacity efficiency, as RAID 6 has less protection data overhead and there is less need for continued fast access to data during RAID rebuild periods.

Compellent is adding support for physical hard disk drive transfer to kick-start a replication service to a remote site, saving network bandwidth and time. When replication first starts, an initial full transfer of data is needed, taking up expensive fast bandwidth or needing days to complete with cheaper, slower network bandwidth. Compellent's software copies data to USB-connected external drives, setting them up as portable volumes. They're then despatched by road, rail or air to a remote Compellent site, with Series 20 or 30 controllers, where they are recognised as portable volumes, ingested and turned into replication target files.

Users embracing Compellent-based cloud storage could like this feature, as they can start off cloud-based replication with a relatively quick and easy sneakernet drive transfer, rather than initially trickling their full data set up to to the cloud in a multi-week, even multi-month exercise.

Storage Centre 5 virtualises an array's I/O ports so the number of physical ports needed in network switches and Compellent controllers could be cut up to a half. Fibre Channel or iSCSI connections can be shared or moved between array controllers should one controller fail. It cuts the cost of having high availability port features for an array.

Another feature is provision for mapping dozens of thinly-provisioned virtual servers at once using a combination of scripting and GUI operations. Compellent has also extended its consistency group protection feature. Fine said: "Now we can do this for non-VSS compatible apps." What happens is that, say, I/O to an Oracle database is temporarily suspended, all the volumes for that database app, up to 40 of them, snapshotted in a consistent state, and the I/O restarted. If the database needs to be restored to a recorded point in time, then a consistency group replay operation is started to bring the database state up to its consistent state at that time.

Compellent's customer sysadmins will like the time-saving and cost-saving features of this release, while its competitors will find it harder than ever to prise these customers away from Compellent and onto their offerings.

Storage Center 5.0 is available immediately through Compellent's channel. ®