Hello Tom, Tuesday, May 23, 2006, 10:37:31 PM, you wrote:
TG> Robert Milkowski wrote: >> Hello Tom, >> >> Tuesday, May 23, 2006, 9:46:24 PM, you wrote: >> >> TG> Hi, >> >> TG> I have these two pools, four luns each. One has two mirrors x two luns, >> TG> the other is one mirror x 4 luns. >> >> TG> I am trying to figure out what the pro's and cons are of these two >> configs. >> >> TG> One thing I have noticed is that the single mirror 4 lun config can >> TG> survive as many as three lun failures. The other config only two. >> TG> I am thinking that space efficiency is similar because zfs strips across >> TG> all the luns in both configs. >> >> TG> So that being said. I would like to here from others on pro's and cons >> TG> of these two approaches. >> >> TG> Thanks ahead, >> TG> -tomg >> >> TG> NAME STATE READ WRITE CKSUM >> TG> mypool ONLINE 0 0 0 >> TG> mirror ONLINE 0 0 0 >> TG> /export/lun5 ONLINE 0 0 0 >> TG> /export/lun2 ONLINE 0 0 0 >> TG> mirror ONLINE 0 0 0 >> TG> /export/lun3 ONLINE 0 0 0 >> TG> /export/lun4 ONLINE 0 0 0 >> >> TG> NAME STATE READ WRITE CKSUM >> TG> newpool ONLINE 0 0 0 >> TG> mirror ONLINE 0 0 0 >> TG> /export/luna ONLINE 0 0 0 >> TG> /export/lunb ONLINE 0 0 0 >> TG> /export/lund ONLINE 0 0 0 >> TG> /export/lunc ONLINE 0 0 0 >> >> >> In the first config you should get a pool storage with capacity equal to >> '2x lun size'. In the second config only '1x lun size'. >> So in the second config you get better redundancy but only half >> storage size. >> >> TG> Ok I see that, df shows it explicitly. [EMAIL PROTECTED]>> df -F zfs -h TG> Filesystem size used avail capacity Mounted on TG> mypool 2.0G 39M 1.9G 2% /mypool TG> newpool 1000M 8K 1000M 1% /newpool TG> What confused me is that ZFS does dynamic striping and if I write to the TG> 2x lun mirror all of the disks get IO. But my error in thought was in TG> how the data gets spread out. It must be that the writes get striped for TG> bandwidth utilization but the blocks and their copies are not spread TG> across the mirrors. I'd like to understand that better. TG> It sure is good to be able to experiment with devious. Well, mirror A B mirror C D with zfs is actually behaving like RAID-10 (stripe over mirrors). The main difference here is variable stripe width but when it comes to protection it's just RAID-10 + checksums for data+metadata. You can imaging such a config as stacked raid - the same if you have created two mirrors on HW RAID, then exposed two such disks to a host and then just did striping using ZFS (zpool create pool X Y - where X is one mirror from two disks and Y is another mirror from two disks). The difference is in using variable stripe width and checksums (and more clever IO scheduler?) -- Best regards, Robert mailto:[EMAIL PROTECTED] http://milek.blogspot.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
