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What's the caveats in using VMFS extends on top of RAID-5 ?

jjoz
jjoz asked
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Last Modified: 2012-08-14
Hi All,

I've got Dell Server with 6x SATA 450 GB HDD configured with RAID-5
so approximately the total capacity is (6x450)-450 = 2.25 TB

for the above datastore I want to use as one single datastore by using multiple extends, can anyone suggest me is there any caveats or performance penalty in using one large datastore on top of RAID-5 disks ?

Thanks,

JJ
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the purpose of this datastore is to server as the backup repository of all the SAN VMs image so i wonder what would happens if one of the disk got failed, would I lose the whole datastore ?
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If one disk fails, you're fine - that's the idea of raid 5.  You'd only lose the lot if you lost two disks before the array had rebuilt onto a new drive.

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wow that's scary, is there any way to get the data back if something happens on the first extends ?
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The only way to recover VMs is if you have a VM b/u solution, using Veeam, vRanger, or some tool like that. But that requires you to have a minimum of vSphere Essentials for the API to backup VMs.

~coolsport00

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Commented:
thanks for the suggestion coolsport, my plan is to have one Windows Server 2008R2 Vm to contains 2 TB VMDK which is being used as the backup container of all the other VM in my SAN, I'd like to know what might be the problem in terms of performance and reliability if there is any.

seems that I involve so many layer in here:
RAID-Layer
VMFS Layer + extends
VMDK
NTFS inside VM
Backup VM files
then files inside the VM
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Well...RAID is the "backbone" solely. VMFS is just the file format and everything else are just files (minus the NTFS partition file format of 1 VMDK, but even then it's still just a file [vmdk] with NTFS  formatting). If you're concerned more about performance, rather than the amt of storage you have, you should consider RAID10.

~coolsport00
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Thanks Mr. bgoering,

so in this case
RAID - 5 is for the application that requires good read and not bothering the write performance
RAID - 10 is for the application that requires both good read and write performance
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thanks for all of th explanation guys,
so now I understand the concept behind RAID :-)

the attached picture might be a "de javu" for some of you here since i got it also for my other thread, however after i read this topic the Random IO is the most important thing here for VMware.
iSCSI-BlockIO-WriteThru.jpg

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Commented:
the above picture is showing the benchmark through the iSCSI to the Openfiler VM on my VMware ESXi.

i ran the DIskSPeed on my physical Windows server 2003 which connects using iSCSI to the OpenFiler 2.3

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thanks guys for the explanation !
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