5

I've managed Dell's EMC and Equallogic SANs in the past. I was recently put in charge of a Hewlett-Packard P2000 SAN. HP and EMC use slightly different terminology. I'd like to confirm I understand HP's terminology. Can you verify/correct some of the definitions below?

vDisk. A collection of physical disks grouped into a RAID array. EMC refers to these as "Storage Pools." vDisks and Storage Pools aren't exactly the same as "RAID groups," but they serve the same purpose.

Volume. A logical division of a vDisk, which is presented to a host as a single volume. EMC refers to these as "LUNs", and LUN is the proper term.

Storage Groups. Distinct from "Storage Pools," EMC SANs can define "Storage Groups," which can combine multiple LUNs into a single volume that's presented to hosts. I can't find an equivalent to this on HP SANs.

Global Spares. Physical hard drives that are not assigned to any vDisk. If a hard drive in a vDisk fails, the SAN automatically uses an available spare to replace the drive and make the vDisk fault tolerant. EMC refers to these as "hot spares." With both vendors, spares do not need to be assigned to a particular RAID group or vDisk. The SAN will use them for any failed hard drive.

Regarding Equallogic SANs: Equallogic arrays create one RAID group and one LUN from all available disks in the array. The administrator can select only: the type of RAID in the RAID group, and the number and size of Storage Groups presented to the hosts.

I think I have these terms right, but I'd like to verify with someone who's used both vendors' SANs. I'm especially concerned that I can't find HP's equivalent of Storage Groups. Surely HP has a way to combine multiple LUNs into one logical volume. Am I missing that setting somewhere?

1

If this P2000 is anything like my old MSA4400, then vDisks are volumes that are assigned to servers as LUNs, but under the covers, what is happening on the HP has little in common with a Clariion.

The way I remember it, the HP has a bunch of disks that it sets up in fixed groups (with RAID, I think), and then vDisks are created that live on these disks with their own virtual raid. So you could have one vDisk with virtually raid 10, meaning each block or chunk that comprised the vDisk would be saved twice, and another one with virtually raid 5, meaning that the chunks would get saved once, but would have distributed parity.

I'm a little hazy on the details about the actual disks, whether there was raid under all these vDisks or just a JBOD. I do remember that we had global spares, because we had several dozen disks of about 100 fail over the course of three weeks, and the system was able to take the hits until more than 9 were rebuilding at the same time.

Maybe someone with more recent and specific P2000 experience can chime in here and help, but this is what I remember.

0

I can only answer the EMC part..

  • Storage Pool: A collection of one or more disk tiers, where each tier can have different RAID levels. The "new" way of doing things.
  • RAID Group: The oldschool way.. It's basically a group of disks in RAID that can be carved into LUN's
  • Storage Group: An administrative collection of both hosts and LUN's. It doesn't do any data operation, it just makes life easier when you want to add a new server to a cluster.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.