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My gut says disabling write cache on soft RAID5 is the smart move, but I'm not certain.

Possible Considerations:

  • The drives a WD20EARS with 64Mb cache.
  • The server hasn't gone down due to a power outage in the last 4-5 years. (even without a UPS)
  • Most of the data is media that can be ripped again from cd/dvd or downloaded from the relevant service, but some of it is pretty critical (family photo's, personal docs etc, but there is a working backup that's tested for recovery twice a year).

What are the pro's and con's of each decision?

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1 Answer 1

up vote 2 down vote accepted

Enabling

Pros: it's faster.

Cons: with RAID5 you can have horrible corruption failures with write cache, when kernel thinks everything is written to disk, and it is safe to continue. Basically, you can get your whole array destroyed unrecoverably (or actually, it is possible to recover, but it is huge mess). We had that case earlier when battery backup for write caches failed (raid card memory backup), and it wasn't nice.

Disabling

Cons: small performance hit for writing.

Pros: your data is safer.


Considerations

Your usage looks like mainly reading (you aren't adding new CD's/DVD's all the time, are you, same goes for family photos etc.). Is it important to have little bit more performance for writing?

How long it will take to rip all data again, and restore all backups in case of failure? If that is trivial amount of time (or someone else will do it :)) go for it, but if you really do not want to do that, I would skip adding small performance improvement.

Also, you can enable write cache temporarily, and run some benchmarks, for example bonnie++ or just copy'n'paste some files to disk to see if there is any advantage. If you can't notice it, is it worth of risks?

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Yep, thats what I thought was the case, i just wanted someone to verify it for me. –  fenix Feb 16 '11 at 21:26

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