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Environment:

  • Storage: HP P2000 MSA G3 SAS Array with 24 300GB 10k SAS Disks
    • Two Storage Controllers with redundant SAS connections to each host
  • Hosts: Three HP DL380 G7s with a 10GB SD Card, CPU, Ram, etc...

ESXi 5.0 is installed on the SD card in each host, this is the only local storage on each host. I have the P2000 split into two vDisks, each using 12 of the 24 disks. Call them LUN1 and LUN2. Each LUN is its own RAID6 volume.

I spoke with HP support over the phone about layering RAID1 over my two RAID6 arrays. This is not possible, so I'm trying to figure out what the best way might be to implement mirroring. I was looking at OpenFiler and FreeNAS, but honestly don't know how those solutions would work in a mission critical application.

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    Why do you want RAID1 on top of your RAID6 arrays? What problem are you trying to solve and what is your desired result?
    – ewwhite
    May 25, 2013 at 20:58
  • Desired result is ability to survive many disk failures. RAID6 gives me the ability to lose 2 disks per vDisk and still be okay. Applications that the servers run cannot go down. This is most important. Performance isn't much of an issue because the system is small. Right now I'm using Storage vMotion to move VMs off of a LUN with a bad disk, so that disk reconstruction performance doesn't affect performance.
    – Lucretius
    May 25, 2013 at 21:06
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    I'd rather have a RAID rebuild cause array stress than a storage vMotion.
    – ewwhite
    May 25, 2013 at 21:45
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    @Lucretius Most RAID controllers do a good job of making the load from disk resilvering a lower priority than real I/O work, so that the impact is minimal; have you seen actual problems from this? Is it realistic that you'll actually have 3 disk failures before you have an opportunity to get a spare rebuilt into the array? May 25, 2013 at 21:56
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    I'm wondering why you need this RAID setup. The chances of triple drive failure are in the realms of winning the lottery twice in one day then being struck by lightning twice. Have a couple cold-spares handy and decent monitoring.
    – Nathan C
    May 28, 2013 at 15:15

1 Answer 1

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There's no software RAID option for the setup you've described.

VMware won't support it. If your hosts were Linux/Windows, you'd have some additional options.

If your concern is system stability, you could have used RAID 1+0 and/or designated hot-spare drives in your setup.

If performance isn't a concern (e.g. the use of RAID6), why worry about the potential impact of a RAID6 rebuild? RAID6 on enterprise SAS drives is usually deemed overkill (versus RAID5) because of the quick(er) rebuild times than nearline/7,200rpm disks. However, you're also doing this across a larger group of disks than normal (12 drives is a lot for that RAID level).

Why stress the system with a Storage vMotion away from the faulted LUN? These are standard HP SAS disks. They don't fail so often that you can't get a replacement in place in a timely manner.

But the best insurance here is to have a hot-spare disk configured and maybe a cold-spare drive handy to reduce the amount of time it takes to replace a disk.

Have you had a drive fail on this array before?

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  • When I say "performance isn't much of an issue" I'm talking about the performance between RAID 10 and RAID 6. RAID 10 outperforms RAID 6, but I feel like RAID 6 is safer than RAID 10.
    – Lucretius
    May 25, 2013 at 21:19
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    We've all had disks fail before. It's why you a) have backups, and b) redundant systems, and c) load balancers for truly mission-critical services. Because while drives are important, it doesn't do you a bloody bit of good when the backplane shorts on your single-server application.
    – Magellan
    May 25, 2013 at 22:33
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    @Lucretius unless your datastore is significantly smaller than the array you've created, it is the same kind of stress - all functioning disks are read once, the replaced disk is written once. The parity calculation does not have any impact on the drives' failure risk and should not impact the performance of the controller too badly either.
    – the-wabbit
    May 28, 2013 at 14:50
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    @Lucretius Sorry to appear rude. It just seemed like you were complicating the situation by focusing on the wrong solution. A spare drive is way handier than the manual work of svMotion or adding another abstraction layer. Disk failures are easy to prepare for and remedy.
    – ewwhite
    May 28, 2013 at 14:56
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    @Lucretius if you really need mirroring across the two vDisks, the way to go seemingly would be to expose both of them as data stores to vSphere, create virtual disks on both and use software mirroring in the guests' OS instances. vSphere/ESXi is rather forgiving about datastore outages in terms that it would not switch off or stall your VMs, but the scenario would require thorough testing nonetheless. If you have an environment which is already in production, this might not be the time for testing though.
    – the-wabbit
    May 28, 2013 at 15:02

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