RAID array with expanded storage

[DVDWSN]

Has anyone used ESXi with a RAID adapter that's capable of Online Capacity Expansion? Meaning, the ability to add new drives to an existing array without having to reformat or redefine the array.

I'm thinking of installing an Adaptec 5805Z. But the plan is to start it with only 4 drives, then expand to 8 over time as the storage needs grow.

How will ESXi handle the RAID Array size change?

[dquintana]

Hello, if you need to expand the disk array, generally the controllers allows you to do the process without stop anything, but the process takes a lot of ours. When the process finishes you can see in the ESX free space to create a new VMFS (datastore) o expand it using extents. I did not recomend to use extent, if you can, move de vms to another storage, then reformat the vmfs to full space.

regards.

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[mcowger]

Actually, ESX4 gracefully handles expanding a VMFS on the fly without using extents in this manner.

--Matt

VCP, vExpert, Unix Geek

[DVDWSN]

Mcowger that's good news. The final array is going to be several dozen TB, so copying it off to rebuild the array would not be practical.

Could you point me towards some documentation on this feature and how to use it? Is there a name for this feature? If so I'll search for docs.

[mcowger]

Note that ESX doesn't support LUNs over 2TB.....

You are going to have to split that up...theres no real name for the feature - you just expand the LUN at the array/storage level, then going into the datastore properties and click expand.

--Matt

VCP, vExpert, Unix Geek

[DVDWSN]

You mean I'll have to split the array? Or just make (at most) 2TB datastores?

[mcowger]

The LUNs you present needs to be under 2TB each.

--Matt

VCP, vExpert, Unix Geek

[DVDWSN]

I found this thread (http://communities.vmware.com/thread/179959) after I posted.

In that thread you mention using RDM. Is that a good solution for me? I was reading elsewhere that there aren't any significant performance differences.

Are there any major drawbacks to using RDM? Dangers?

Would that allow me to setup a guest with larger than 2TB drives?

Can a you still have other Guest's store their VMDK's on the drive that's being accessed by RDM, or does it have to be dedicated?

[dquintana]

You can expand but take care the limit is 2TB.

[mcowger]

RDM isn't a solution with local disks, and still limits you to 2 TB.

If you want to setup a guest with that much space from local disks,

you need to create multiple exports (aka LUNs) from your array, each

less than 2 TB, put a large VMDK on each one for your guest, and then

use whatever striping software your guest supports to strip all the

devices into 1 large one.

--m

[admin]

Why RDM is not a solution. It should work. You can take any LUN or partition and assign to a VM. In which ase there shouldn't be 2TB limitation since guest sees the LUN as it is.

[mcowger]

So, it IS possible with certain combinations of guest OSs and physical mode RDMs, however it is still explicitly not supported. Better to stick with a supported config.

--Matt

VCP, vExpert, Unix Geek

[admin]

Where does it say it is not supported. RDMp is a supported configuration.

[mcowger]

Not over 2TB it isn't:

http://www.vmware.com/pdf/vsphere4/r40/vsp_40_config_max.pdf

See the bottom of page 2.

--Matt

VCP, vExpert, Unix Geek

[admin]

I don't think RDMp suffers by this.

[mcowger]

Like I said - it does actually work with RDMp, but officially its not supported (meaning not that it doesn't work, only that vmware support may chose not to help you when it breaks).

That document is the canonical answer on whats supported, and it doesn't specify which kind of RDMs, so it applies to all RDMs.

--Matt

VCP, vExpert, Unix Geek

[admin]

I will talk to some folks to see if we can fix this by using different terminologies.