Monthly Archives: July 2014

Symmetrix offers a new kind of MAXimum Virtualisation (VMAX)


The mother of all arrays has just been given an upgrade!

Well ok, maybe EMC did not produce the mother, since it’s fair to say IBM 3390 disk subsystem came first, but since the first Symmetrix came out in the early 90s with as much as a dozen or two disks, EMC has come a long way. They set the standard when it came to enterprise storage arrays. And it wasn’t just size that mattered back then: performance was and is still the number one objective for the Symms. After the “dark ages” (roughly before the year 2000) things got serious with the DMX series in 2003. The number of disks went up and loads of cache had to make sure that performance was guaranteed. DMX1, DMX2, DMX3/4 were quite a success.

And then there was VMAX

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Increased response times on VNX when using Windows 2012

Windows 2012 can cause higher response times on VNX

When Windows 2012 issues Trim or Unmap commands to thin LUNs on a VNX, the Storage Processor response times can increase or may initiate a bugcheck.

As part of disk operations to reclaim free space from thin LUNs, Windows 2012 Server can issue large numbers of the SCSI command 0x9E/0x12 (Service Action/Get LBA Status). This SCSI command results in what is called a “DESCRIBE_EXTENTS” I/O on the VNX Storage Processor (SP.) These commands are used as part of the Trim/Unmap process to see if each logical block address (LBA) that has been freed up on the host’s file system is allocated on the VNX thin LUN. The host would then issue Unmap SCSI commands to shrink the allocated space in the thin LUN, thus freeing up blocks that were no longer in use in the file system. RecoverPoint also issues these same SCSI commands when the Thin LUN Extender mechanism is enabled, which can cause similar performance issues. See knowledge base article KB174052 for more information about the RecoverPoint variation of this issue and how to prevent it.

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