Got a call at 4am - RAID Gurus Please Read

Javier J javier at
Wed Dec 10 22:18:49 UTC 2014

I'm just going to chime in here since I recently had to deal with bit-rot
affecting a 6TB linux raid5 setup using mdadm (6x 1TB disks)

We couldn't rebuild because of 5 URE sectors on one of the other disks in
the array after a power / ups issue rebooted our storage box.

We are now using ZFS RAIDZ and the question I ask myself is, why wasn't I
using ZFS years ago?

+1 for ZFS and RAIDZ

On Wed, Dec 10, 2014 at 8:40 AM, Rob Seastrom <rs at> wrote:

> The subject is drifting a bit but I'm going with the flow here:
> Seth Mos <seth.mos at> writes:
> > Raid10 is the only valid raid format these days. With the disks as big
> > as they get these days it's possible for silent corruption.
> How do you detect it?  A man with two watches is never sure what time it
> is.
> Unless you have a filesystem that detects and corrects silent
> corruption, you're still hosed, you just don't know it yet.  RAID10
> between the disks in and of itself doesn't help.
> > And with 4TB+ disks that is a real thing.  Raid 6 is ok, if you accept
> > rebuilds that take a week, literally. Although the rebuild rate on our
> > 11 disk raid 6 SSD array (2TB) is less then a day.
> I did a rebuild on a RAIDZ2 vdev recently (made out of 4tb WD reds).
> It took nowhere near a day let alone a week.  Theoretically takes 8-11
> hours if the vdev is completely full, proportionately less if it's
> not, and I was at about 2/3 in use.
> -r

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