| From: | david(at)lang(dot)hm |
|---|---|
| To: | Mark Mielke <mark(at)mark(dot)mielke(dot)cc> |
| Cc: | Florian Weimer <fw(at)deneb(dot)enyo(dot)de>, Fernando Hevia <fhevia(at)ip-tel(dot)com(dot)ar>, "'pgsql-performance'" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: With 4 disks should I go for RAID 5 or RAID 10 |
| Date: | 2007-12-26 23:38:34 |
| Message-ID: | Pine.LNX.4.64.0712261536440.11785@asgard.lang.hm |
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| Lists: | pgsql-performance |
On Wed, 26 Dec 2007, Mark Mielke wrote:
> david(at)lang(dot)hm wrote:
>> I could see a raid 1 array not doing consistancy checking (after all, it
>> has no way of knowing what's right if it finds an error), but since raid
>> 5/6 can repair the data I would expect them to do the checking each time.
> Your messages are spread across the thread. :-)
>
> RAID 5 cannot repair the data. I don't know much about RAID 6, but I expect
> it cannot necessarily repair the data either. It still doesn't know which
> drive is wrong. In any case, there is no implementation I am aware of that
> performs mandatory consistency checks on read. This would be silliness.
sorry, raid 5 can repair data if it knows which chunk is bad (the same way
it can rebuild a drive). Raid 6 does something slightly different for it's
parity, I know it can recover from two drives going bad, but I haven't
looked into the question of it detecting bad data.
David Lang
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