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List:       freebsd-hackers
Subject:    Re: gvinum status?
From:       John-Mark Gurney <jmg () funkthat ! com>
Date:       2014-06-27 11:43:19
Message-ID: 20140627114318.GE1560 () funkthat ! com
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Michael W. Lucas wrote this message on Wed, Jun 25, 2014 at 08:48 -0400:
> Back in the day, vinum was a big deal. It's been replaced by
> gvinum(8). And gvinum is the only in-base way to do OS-based RAID5.

Well, there is at least one geom raid5 out there, just not in the base
system:
http://www.wgboome.org/geom_raid5-html

Though doesn't look much up to date...

> But I don't hear much about it.
> 
> Is gvinum discouraged or slated for deprecation? Or is it merely less
> popular now that everyone's jumped on the ZFS train?

The problem w/ raid5 is that unless you have a battery backed cache,
or a log, or something, you can end up corrupting your data...  So,
after a power crash, you have to rebuild all pairty, since you don't
know which stripe didn't make it entirely to disk...  If you don't
rebuild and the parity made it to disk and the data didn't, a future
data disk lose will corrupt the data on that stripe...  And a rebuild
after every power lose is a big cost, plus, what happens if the stress
of the rebuild causes a disk to die?

w/ ZFS and it's COW and raidz being more like RAID3, you never have to
worry about the issues above..

So, if you care about your data, you don't do software RAID5, so what's
the point of it then? :)

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."
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