On Thu, Jun 03, 2010 at 12:40:34PM -0700, Frank Cusack wrote: > On 6/3/10 12:06 AM -0400 Roman Naumenko wrote: > >I think there is a difference. Just quickly checked netapp site: > > > >Adding new disks to a RAID group If a volume has more than one RAID > >group, you can specify the RAID group to which you are adding disks. > > hmm that's a surprising feature to me.
It's always been possible with Netapp. Back in the pre-5.0 (maybe it was pre-4.0) days, an OnTAP device only had one raid group and one filesystem/volume. All you could do was expand it, not add additional raid groups or additional volumes. When the other features were added, the ability to expand a raid group was not removed. > I remember, and this was a few years back but I don't see why it would > be any different now, we were trying to add drives 1-2 at a time to > medium-sized arrays (don't buy the disks until we need them, to hold > onto cash), and the Netapp performance kept going down down down. We > eventually had to borrow an array from Netapp to copy our data onto > to rebalance. Netapp told us explicitly, make sure to add an entire > shelf at a time (and a new raid group, obviously, don't extend any > existing group). Yup, that's absolutely the best way to do it. Otherwise, all your writes will be on the one or two new disks creating hotspots until you can rebalance your data, and that could take a long time. I'm pretty sure in the distant past, they had no online rebalancer. Nowadays there is one, but it's not particularly speedy. Think adding a mirror pair to a large, nearly-full zpool. The same thing will happen. -- Darren _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
