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Drives are very cheap these days. Would it be worth it to increase the group size from 2 to 3. I found 1TB drives for $60. I feel as if the array is very vulnerable to failure in a 2 group setup since drive failures are tightly correlated and it would be worth adding another drive to each RAID 10 group for the added redundancy (all 3 drives per group have to fail). Am I better off going this route, or sticking to a 2 drive per group setup. What would be considered "best practice".

Basically:

1TB
1TB

1TB
1TB

1TB
1TB

-vs-

1TB
1TB
1TB

1TB
1TB
1TB

I like RAID 10 setups due to their simplicity.

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  • What is the general use for this host? This will have an effect on the responses offered.
    – AngryWombat
    Aug 15, 2013 at 22:08
  • Just for regular storage such as user profiles or backups. What I'm trying to say is that yes I can get get 1 more TB by doing a 2x3 setup, yet drives are so cheap that who cares I can get the same by doing a 3x3 setup. There is a point where it becomes a waste. Obviously 5 drives in a group is way overkill and a waste of $. I'm asking what that point is.
    – oooooo3333
    Aug 16, 2013 at 12:52
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    "since drive failures are tightly correlated" -- Needs reference
    – Chris S
    Aug 21, 2013 at 14:13

2 Answers 2

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If you're looking to be able to withstand double-drive failures to any disks in the array (not possible with two-member-per-mirror RAID 10s), you may want to consider RAID 6 instead.

As for what is "best practice" I'll say that you almost never see a triple mirror anywhere.

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  • 1
    ZFS triple-mirrors. Sometimes we do it for read performance.
    – ewwhite
    Aug 16, 2013 at 22:09
  • Triple mirror seems like such a good strategy. RAID 6 is a more complicated setup, has long rebuild times, is taxing on the hardware, and there are hardly any drive recovery tools for it. Why doesn't anyone tipple mirror?
    – oooooo3333
    Aug 21, 2013 at 13:25
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    Almost no one triple mirrors because it's wildly inefficient. If you need such high availability, usually people start clustering storage nodes at that point. RAID 6 isn't any more complicated to configure than RAID 10 and it is not taxing to a dedicated RAID controller - they have built-in XOR processors just for RAID 5 and RAID 6 parity calculations and the write penalty is negated by properly sizing your write cache. As far as drive recovery tools goes - they should not matter. You should be using proper backups and not relying on dodgy software-based data recovery tools.
    – MDMarra
    Aug 21, 2013 at 13:46
  • @oooooo3333 (proper, useful) triple mirroring is more complex to set up than RAID 6. If your application isn't speed-critical the performance difference will be negligible (and you're using $60 1TB disks, which says "consumer-grade SATA" to me, so I'm going to go out on a limb and say whatever you're doing can't be speed-critical).
    – voretaq7
    Aug 21, 2013 at 13:56
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    Not a hobby project I'm helping someone out and I don't think they NEED to spend thousands of dollars to get a good setup (it's a win server with roaming profiles). I also wanted to use this for their backup NAS. I want a nice cheap redundant setup, that's all. This isn't a database that is getting hit millions of times per day. I'm trying to help them out and save them $. I was just under the assumption a RAID 10 has pretty good performance and redundancy. I thought I could boost the redundancy a little more by triple mirroring.
    – oooooo3333
    Aug 21, 2013 at 14:23
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"Triple mirroring" is what you're speaking of.

The ability to execute this is a function of your RAID controller setup and/or software capabilities.

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2
  • I'm not asking if it can be done. I'm asking if it's worth it from a price perspective. Obviously 5 drives in a group is way overkill and offers no more benefits than 4 drives on a price perspective. There is diminishing marginal utility to adding new drives to a group.
    – oooooo3333
    Aug 16, 2013 at 12:52
  • @oooooo3333 You haven't provided enough detail as to what equipment you're using... Disk type/make/model, controller type, hardware RAID, software RAID, operating system... So um, there's not much to say without that information.
    – ewwhite
    Aug 16, 2013 at 13:03

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