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spgsit5upport
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Backup of large RDM

Post by spgsit5upport »

I have one (fileserver) VM that has 4 separate RDM disks on iSCSI array (ranging from 350Gb to 2Tb)

What would be the "best" option to back them up? vRDM (currently all are pRDM), forward incremental?

Ofcourse I can do file backup with Arcserve agent inside VM, but it does take a good while to run
Also ability to restore a single file would be required (something that can be easily done with Arcserve).

The filesystem is Novell NSS

Seb

Jfmoots
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Re: Backup of large RDM

Post by Jfmoots »

Is your proxy server physical or virtual? What type of iSCSI array are you talking about?

Here's my thoughts... If your server is virtual, you can use hot add to back up vRDMs. To me, that's the most efficient method if you're going to positively use RDMs.

If your proxy is physical, I think you'd be best making them VMDKs. To the best of my knowledge, we still can't use SAN Mode to back up a vRDM. As a result, we'll resort to network mode and that would be not fun at all for backing up those large volumes.

Any compelling reason you need to use RDMs?

spgsit5upport
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Re: Backup of large RDM

Post by spgsit5upport »

I feel that performance from RDM is better then vmdk

According to FAQ vRDM can be backed up, as it can be snapshot

Seb

dellock6
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Re: Backup of large RDM

Post by dellock6 »

Basically everything that can be snapshotted can also be backed up ;)
About performance differences, we are talking about 1-2% at best between RDM and VMFS and not in all cases; if it not for creating MS clusters on VMs, or going over 2 Tb with ESXi 5.0 RDMs, I do no see any other reason to stay with pRDM.
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Jfmoots
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Re: Backup of large RDM

Post by Jfmoots »

spgsit5upport wrote:I feel that performance from RDM is better then vmdk
While that used to be the case, I think it's a great subject to argue :)
spgsit5upport wrote:According to FAQ vRDM can be backed up, as it can be snapshot

Seb
Absolutely. No argument there. However, HOW you back it up is important to consider. We back up in 3 modes: Direct SAN, Hot Add, and Network. Direct SAN is good because it talks directly to the storage on only impacts the host as far as snapshots go. Hot add is next best because it reads the VM via the storage i/o stack on the Hypervisor (this is much faster than the alternative). Network mode is the least desirable because everything is going acrosst he Hypervisor's network i/o stack and across your LAN. Network mode works... but if you can architect things so you don't have to use it, you're in a better boat.

You asked for the "best" option :)

Gostev
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Re: Backup of large RDM

Post by Gostev »

Luca is right, the performance benefit of using RDM is not measurable in most cases. However, by not virtualizing your storage you are loosing about 50% of goodness that virtualization brings to the table.

Also, just a small note on the Network processing mode - it is awesome with 10 Gb Ethernet.

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