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I have a Dell PowerEdge 2970. Currently it runs as a ESXi server with a handful of VM's on it. I have 3 300GB drives plugged in to it, and 5 open trays across the front. It is setup as a hardware Raid5 from the factory. My question is if I start running low on disc space, can I just add on by pushing another hard drive into a empty slot, or will I need to back everything up and rebuild the array? If I can't just plug in another hard drive, would it be better to add 3 more drives, and build a second Raid5 to avoid losing any data that I have

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did some hunting around. I have 3 300GB 10,000RPM drives. The controller is a PERC 6/i Integrated. – Skaughty Jan 27 '10 at 15:56
up vote 3 down vote accepted

I couldn't disagree with joeqwerty more to be honest. You don't mention which controller you have but all of the PERC 5 and 6 cards can perform live array expansion, although I'd be strongly tempted to fully backup your volume first. This way your new drive/s will become part of the R5 array and so will be able to survive a single disk failure. If you simply add another extent then in the event of losing a disk you stand a good chance of losing the whole VMFS datastore (the risk lessening if you're on ESX/i v4), plus expanding the array to 6 drives gives you 300GB more space than two 3 drive arrays.

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+1 Great points! – Dave M Jan 27 '10 at 15:08
Ouch. Good points. My way is one way, but may not be the best way (but it probably is the simplest). – joeqwerty Jan 27 '10 at 17:28
to be honest I've only ever live expanded HP controllers, which I trust a lot more than PERCs, but they have worked each time - even though I was very nervous – Chopper3 Jan 27 '10 at 17:30
It's worth noting that not all RAID cards can do live expansion. I spent quite some time talking to LSI, and the rep was very careful to explain that when expanding an R5 array, the array cannot be used until the rebuild finishes. – tylerl Oct 6 '10 at 1:24

The simplest thing to do might be to create a new RAID5 array and add it to the VM datastore as a new extent.

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If your storage needs hold out long enough to get a whole new server, that's what I'd do instead, but if you get squeezed then the "safe" route is probably adding a new datastore. Some controllers will let you "grow" the volume, others not, others are supposed to allow it but there's a chance something will go kerplooey so you'd end up backing up and restoring anyway (especially with RAID 5 issues and unrecoverable disk errors...BIG issue now...we were bitten by it on a dell server with RAID 5) – Bart Silverstrim Jan 27 '10 at 14:56

To anyone else looking at this:

On the older PERC 5 cards you could just pop the drives in and run a reconstruction in the RAID BIOS to add capacity or do a Raid Level Migration (RLM)

On the PERC 6 you'll need to install the Open Manage Server Administrator. It takes a few extra steps when installing on ESXi, but it's worth it. You can expand a live array without any interruption in service. Although be aware that it does take a looooonnnnnggg time to rebuild the array after adding a drive (plan 4-6 hours at least), and during the rebuild you'll have degraded service.

  1. Shut down all hosts and install OMSA, then enable CIM using the steps outlined -> OMSA install on ESXi
  2. Then in order to access OMSA install the Managed Node Admin Tool on a separate station. (Can’t just use htps://server:1311)
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Depends on the RAID controller to grow the volume and depends also on the OS to resize the partition and grow the filesystem. Check the documentation for your RAID controller and the documentation about VMFS.

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