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.
Ok I see that, df shows it explicitly.
[EMAIL PROTECTED]> df -F zfs -h
Filesystem size used avail capacity Mounted on
mypool 2.0G 39M 1.9G 2% /mypool
newpool 1000M 8K 1000M 1% /newpool
What confused me is that ZFS does dynamic striping and if I write to the
2x lun mirror all of the disks get IO. But my error in thought was in
how the data gets spread out. It must be that the writes get striped for
bandwidth utilization but the blocks and their copies are not spread
across the mirrors. I'd like to understand that better.
It sure is good to be able to experiment with devious.
-tomg
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