On Mar 25, 2010, at 12:10 PM, Freddie Cash wrote:
> On Thu, Mar 25, 2010 at 11:47 AM, Bruno Sousa <bso...@epinfante.com> wrote:
> What do you mean by "Using fewer than 4 disks in a raidz2 defeats the purpose
> of raidz2, as you will always be in a degraded mode" ? Does it means that
> having 2 vdevs with 3 disks it won't be redundant in the advent of a drive
> failure?
>
> raidz1 is similar to raid5 in that it is single-parity, and requires a
> minimum of 3 drives (2 data + 1 parity)
no. raidz requires a minimum of 2 drives: data + parity
> raidz2 is similar to raid6 in that it is double-parity, and requires a
> minimum of 4 drives (2 data + 2 parity)
Similarly, raidz2 requires 3 drives: data + 2 parity
>
> IOW, a raidz2 vdev made up of 3 drives will always be running in degraded
> mode (it's missing a drive).
The definition of the degraded state is in the zpool(1m) man page:
DEGRADED
One or more top-level vdevs is in the degraded state
because one or more component devices are offline. Suf-
ficient replicas exist to continue functioning.
One or more component devices is in the degraded or
faulted state, but sufficient replicas exist to continue
functioning. The underlying conditions are as follows:
o The number of checksum errors exceeds accept-
able levels and the device is degraded as an
indication that something may be wrong. ZFS
continues to use the device as necessary.
o The number of I/O errors exceeds acceptable
levels. The device could not be marked as
faulted because there are insufficient replicas
to continue functioning.
-- richard
ZFS storage and performance consulting at http://www.RichardElling.com
ZFS training on deduplication, NexentaStor, and NAS performance
Las Vegas, April 29-30, 2010 http://nexenta-vegas.eventbrite.com
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
