On Mon, Oct 18, 2010 at 3:28 AM, Habony, Zsolt <zsolt.hab...@hp.com> wrote:
> In many large datacenters, a different storage team handles LUN requests > and assignment. > We ask a LUN in a specific size, and we get one. > > It might result that the first vdev (LUN) is on a beginning of a RAID set > on the storage, > and the second vdev is on the end of the same RAID set on the same physical > disks. (If not in the creation time, then > later, during the increase of a filled zpool, by adding a LUN) > > I worry about head thrashing. Though memory cache of large storage should > make the problem > easier, I would be more happy if I can be sure that zpool will not be > handled as a stripe. > > Is there a way to avoid it, or can we be sure that the problem does not > exist at all ? > > -----Original Message----- > From: Darren J Moffat [mailto:darr...@opensolaris.org] > Sent: 2010. október 18. 10:19 > To: Habony, Zsolt > Cc: zfs-discuss@opensolaris.org > Subject: Re: [zfs-discuss] How to avoid striping ? > > On 18/10/2010 07:44, Habony, Zsolt wrote: > > I have seen a similar question on this list in the archive but haven't > > seen the answer. > > > > Can I avoid striping across top level vdevs ? > > > > If I use a zpool which is one LUN from the SAN, and when it becomes full > > I add a new LUN to it. > > > > But I cannot guarantee that the LUN will not come from the same spindles > > on the SAN. > > That sounds like a problem with your SAN config if that matters to you. > > > Can I force zpool to not to stripe the data ? > > You can't, but why do you care ? > > -- > Darren J Moffat > > It shouldn't matter if LUN's are on the same backend disk. Unless the manufacturer of the array is brain dead, their wide striping algorithm should handle it without breaking a sweat. If the pool of disk can't service the number of IOPS, the "storage team" should be moving LUN's around, that's what they get paid to do. Your *issue* shouldn't be an issue at all unless the backend disk is junk. I've never seen an issue with Hitachi's HDP or NetApp's aggregates. --Tim
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