Trying to polish the final fine details of software RAID mission critical home-server solution. I am curious about the server performance in RAID-1 (mirroring) degraded mode (where one of the hard disks failed). Will it make it till the next day (or more) if I am in the middle of finishing some critical project or I am supposed to replace the second disk as soon as possible?

The rationale of the system I've came up with is software RAID (with mirroring) and daily backup. My thought was that if RAID fails then I still can finish the workday (have a last day backup anyway) AND then replace the damaged hard disk. How real/feasible is the scenario?

To clarify, I'm considering to utilize Ubuntu-based software RAID implementation.

PS: if the scenario is totally not feasible, then I can consider replacing RAID-1 by RAID-5. Will it work better?


RAID1 handles degrading gracefully. The only thing you have to worry about when running degraded is, what happens if the second disk dies? Other than that, you can run degraded indefinitely. Read performance may drop to the extent that the machine was previously able to satisfy reads from both disks. Write performance may actually improve slightly.

RAID5 performance drops substantially in degraded mode (but RAID5 needs 3 disks, really). This is because of the parity calculations and extra reads needed to reconstruct the data on the missing disk.

There is no reason you have to stop what you're doing to replace a disk, by the way. SATA hot swap enclosures are fairly cheap. In addition, in environments where reliability is very important, hot spares (extra disks in the machine that are automatically put into the array if a disk fails) can be used—this is more common in enterprise.

  • It's not for the enterprise, but for the home office (with my audio releases, photographic works and graphics projects of my girlfriend). Every 3 years an HDD brings its own surprises and I kinda feel ready to invest for a better sleep. I also understand that RAID5 needs HW controller, so I'll choose mirroring plus backup. The enclosures are usually kinda expensive and I'd prefer a really simple Ubuntu computer which will give nearly same value for twice less money. In case you have other opinion/recommendations on that to share - please do. Thanks again. – BreakPhreak May 18 '11 at 22:47
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    Ummm, SATA hot swap bays are ~$20/bay. Software RAID5 is fine, too, though it'll cost some CPU time (but not really an issue on modern CPUs on non-enterprise systems) – derobert May 20 '11 at 20:01

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