InfoWorld review: Dell iSCSI SAN sizzles with SSD, dynamic storage tiering

The Dell EqualLogic PS6010XVS with automated storage tiering leverages fast SAS or faster SSD storage depending on workload

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Pulling the plug: Redundant controllers and hot spares
During a period of intense utilization on the array, I walked around behind it and yanked out the active controller. Other than the management interface showing that the controller had vanished, nothing else noticed. There were no problems with the active workloads or any other ill effects. Reseating the controller simply brought it back up in the management interface, and everything else carried on normally.

It should also be noted that firmware updates to the EqualLogic PS6010XVS can be carried out without any downtime, as the first controller to be updated will reboot without dropping clients and take on the full load while the secondary completes its update.

How does a split array like the Dell PS6010XVS address the potential problem of disk failure? In a normal array with identical drives, one or two drives would be designated as spares and called into action if a primary drive failed. The SAS side of the PS6010XVS is no different, with one of the eight drives designated as a hot spare. However, there is no hot spare SSD, as all eight are present in the RAID6 array. Thus, an SSD failure will not be able to pull a spare SSD into the mix. Instead, the controller will bring the hot spare SAS drive into the SSD array.

Substituting the SAS drive will necessarily degrade the performance of the SSD array, but also protect the integrity of the data stored on the SSD. When the failed SSD is replaced, the SAS replacement dumps all of its content to the new SSD and resumes its position as a hot spare, so the SSD array will once again be up to full speed. Given the price and higher reliability of the SSD, this scenario is acceptable, but it's wise to keep a cold spare SSD on hand.

The EqualLogic PS6010XVS represents yet another impressive product from Dell. The only downside is the relatively small capacity of the solution. Of the raw 4.4TB capacity, you'll see 500GB of SSD storage and roughly 2TB in SAS storage available for general use. The decision to go with the 450GB SAS drives was made to keep the ratio of SAS to SSD storage around 4:1, helping to maximize the performance enhancements of the SSD. That positions the Dell PS6010XVS not as a general-purpose array, but one that would be best utilized for highly transactional workloads and heavily loaded virtual servers. As with all EqualLogic arrays, the PS6010XVS will fall right into place alongside other EqualLogic units and can be managed from within the same group.

Dell EqualLogic PS6010XVS iSCSI SAN

Cost $55,000 fixed configuration with eight 100GB SSDs and eight 450GB 15K RPM SAS drives, both arrays configured in RAID6
Operating systems supported Windows Server 2000/2003/2008/2008 R2, VMware ESX Server, Citrix XenServer, Red Hat Enterprise Linux, Novell Suse Linux Enterprise Server, Oracle Solaris, IBM AIX, HP-UX, Mac OS X, Novell NetWare

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