Vault Drives on the New EMC VNX Arrays

Let me preface this blog by stating the following information is not all original.  I am simply passing through some of the information on from one of my contacts at EMC.  Normally I wouldn’t plagurize like this but the information is important and you should be at least aware of some of the changes with the new VNX line.

Any of you familiar with EMC arrays such as the Clariion CX4 or Celerra NS lines are or should be very familiar with EMC’s usage and implementation of “the Vault”.  The Vault is where the OS for the array lives.  In the case of Clariion and Celerra we are talking about the FLARE and DART code that enables the array to do its thing.  Up until now this has always been the 1st 5 drives in the array – Drive Slots 0 – 4.  These disks were setup as a 4+1 R5 Raid Group on which the FLARE/DART took up a small about of space on each drive.  The remaining space could be used just not for any high I/O loads.  Drive size was up to you but pretty much any drive size/type would work.

One of the first things I noticed when building my first VNX solution in EMC’s configuration tool what that the Vault drive choices were much different than before.  For the VNX5100 you’re forced to choose 6 drives for the Vault and for the VNX5300 its 8 drives.  In reality the Vault on these arrays only uses 4 drives to store the OS code.  The reason why – according to what I’ve heard its to give the array a better price point – given what I’ve seen so far …. this holds to be true.

Ok, start plagurizm here:

So say you have 300 GB drives in the first shelf, total of 6 drives.

The useable capacity in first 4 (0-3)drives = 300 GB – 192 GB => 108 GB.

Drives 4, 5 useable capacity is full 300 GB, green box shows useable capacity:

This space can be used two ways:

(a) You can use the available space on the first 4 drives for a stand-alone RG or NAS/Block Pool. For example: RAID 5 (3+1) will give you ~324 GB usable AND use the remaining drives as another RG or part of a pool. There is no space wastage in this case.

(b) You can create a RG that spans across all the 6 drives as shown by the black square going across all 6 drives. This gives widest stripe configuration for RAID Group *but* you only get 108 GB of space from all 6 drives and 192 GB on the drive 4 and 5 is wasted.  (I don’t recommend this).

(c) For larger systems assign the extra 2 or 4 drives as hot spares, or as ‘buffer space’ for when the customer needs to add storage in case they wait until they are 98% full to order it.

So as you can see the vault requirements have shrunk from 5 drives to 4 drives but then got jacked up to 6 drives or 8 drives – hey….. makes sense to me.  Basically just plan to use the “extra” drives as part of another storage pool or raid group or just use them as hot spares.

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One Response to “Vault Drives on the New EMC VNX Arrays”

  1. Calvin Says:

    Calfo, I read their Unifield storage doc saying the minimum is 4, may be cust complaint about the ‘forced’ 6 or 8 drives policy.
    ”VNX models require a minumum of four ‘vault’ drives (SAS) and support a maximum of 1000 disk drives in up to 67 disk expansion chassis.”

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