I'm looking for a RAID card on newegg and I was warned not to get a "fake RAID" controller, where the striping, mirroring and parity processes are done on the CPU instead of the controller.

How do I determine if a RAID controller is fake-RAID or not?


Fakeraids don't have battery backed cache. So if power is lost, all write-behind cache data is lost, or controller itself does not go beyond the write speed capabilities of hard drives involved.

E.g., measure write IOPS for hard drives (should be 75-100 for 7200 rpm, 125-150 for 10000 rpm, 175-210 for 15000 rpms). Then test write IOPS for controller. If numbers go high and there's no RAM and battery on board - then it's kind of fakeraid that's unsafe to use.

Personally I recommend ZFS over fakeraid if you can afford to use FreeBSD/OpenSolaris, as it does not require hardware controller, supports bit rot prevention via checksums for user data and metadata, can read from other disk in the mirror if checksum fails (unlike any top-notch hardware RAID), can make materialized-on-disk copy-on-write snapshots, can use SSD as a level 2 cache to speedup read IOPS and has many more features.

You only need $1000 hardware RAID if hundred write IOPS is not enough for your highly-loaded database server. In terms of reliability, it's better to use ZFS and few additional HDDs.

  • 1
    I too stand behind ZFS, its solid and pretty easy to understand. ZFS can be added to Linux. zfsonlinux.org – ianc1215 Nov 14 '11 at 8:17

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