On Tue, Sep 8, 2009 at 10:23 AM, Piero Gramenzi<piero.grame...@sun-cs-italy.com> wrote: > Hi Darren, > >>> I do have a disk array that is providing striped LUNs to my Solaris box. >>> Hence I'd like to simply concat those LUNs without adding another layer of >>> striping. >>> >>> Is this possibile with ZFS? >>> >>> As far as I understood, if I use >>> >>> zpool create myPool lun-1 lun-2 ... lun-n >>> >>> I will get a RAID0 striping where each data block is split across all "n" >>> LUNs. >> >> Individual ZFS blocks don't span a vdev (lun in your case) they are on one >> disk or another. ZFS will stripe blocks across all available top level >> vdevs, and as additional top level vdevs are added it will attempt to >> rebalance as new writes come in. > > That's exactly what I would like to avoid. > > I do have several Solaris servers, each one mounting several LUNs provided > by the same disk-array. > > The disk-array is configured to provide RAID5 (7+1) protection so each LUN > is striped across several physical disks.
So you have a disk array carved into multiple luns on the raid subsystem. Then think about exporting 1 lun per solaris host from the array instead of multiple. I would have a second raid5 (7+1) array carved into identical luns also exported 1 lun per solaris host and setup a mirror vdev on each solaris box between those two luns so there is some redundancy there. > If I was mounting multiple LUNs on the same Solaris box and ZFS was using > them in RAID0 then the result is that each filesystem write would span across > a > *huge* number of physical disks on the disk-array. The 1 lun per host per array should solve that. > This would almost certainly impacting other LUNs mounted on different > servers. It will anyways, so make sure the workloads are complementary. > As the striping is already provided at hardware level by the disk-array, I > would like to avoid to further stripe already striped devices (ie LUNs). > >>> If that's correct, is there a way to avoid that and get ZFS to write >>> sequentially on the LUNs that are part of myPool? >> >> Why do you want to do that ? What do you actually think it gives you, >> other than possibly *worse* performance ? > > ditto. > > Of course the alternative is to get the disk-array providing non-striped > LUNs but I suspect that hardware striping is way more efficient than > software strping, no matter of good ZFS is. Both hardware or software provide equal performance when it comes to striping. -Ross _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
