5

I want to set up a RAID 5 with 3x1TB drives on a Linux KVM-Host. The RAID will be used as LVM thin storage for VM disks.

There has already been much discussion on hardware raid vs software [1]. According to this discussion one should not use software raid but hardware raid with cache and BBU for VM disk storage because of the better write performance.

What I would like to know is if the following setup would be comparable to a hardware raid with cache and BBU (e.g. HP P410 512 MB + BBU) in terms of read/write performance and data safety:

  • Linux Software RAID / mdadm RAID 5
  • LVM writeback cache on a 512 MB ram disk
  • Host backed by UPS to prevent data loss like the BBU on hw raid

[1] Software vs hardware RAID performance and cache usage

9

None from above! You really need to look at ZFS on Linux.

http://zfsonlinux.org

https://www.reddit.com/r/zfs/comments/514k2r/kvm_zfs_best_practices/

Perfect discussion, tons of links.

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    Yeah, I've had a look at ZFS but I don't want to use third-party kernel patches or modules and this doesn't really answer my question. Thanks anyway. – c0d3z3r0 Jul 2 '17 at 18:55
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    The problem is with your config - 5x1TB spinners in RAID5 you're getting to a point where limit of a single parity RAIDs really kicks in. I mean both hardware RAID and LVM are dangerous in terms of a slow rebuilds. ZFS with RAIDZ1 is close to RAID5 but a) rebuilds are faster so less changes to hit double fault and lose all your data, b) there are hashes so silent bit rot isn't going to happen, and c) there's no write hole as ZFS has variable size parity strips. TL;DR: Don't do hardware or software parity RAID with 1TB SATA drives. – BaronSamedi1958 Jul 2 '17 at 19:19
  • Hmm, maybe I should really simply try ZFS... Thank you for explaining the details :-) – c0d3z3r0 Jul 3 '17 at 17:34
  • Best of luck! :) – BaronSamedi1958 Jul 3 '17 at 20:14

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