[lustre-discuss] Expanding a zfsonlinux OST pool

Bob Ball ball at umich.edu
Tue Nov 24 05:25:38 PST 2015

Thanks much for your reply, Olaf.

Below for the answers.

On 11/23/2015 4:35 PM, Faaland, Olaf P. wrote:
> Hello Bob,
> We did something similar - our MDS's used zpools based on spinning 
> disks in JBODs and we switched to SSDs without bringing the filesystem 
> down, using ZFS to replicate data.  It worked great for us.
> How are your pools organized (ie what does zpool status show)? There 
> might be options that are more or less risky, or take more or less 
> time, depending on how zfs is using the disks.
This is a typical pool, which consists of disks on Dell MD1000 shelves, 
each a single-disk raid-0 to make the JBOD group, then assembled via pci 
address into the zpools of 10 disks each.

# zpool status ost-001
   pool: ost-001
  state: ONLINE
   scan: none requested

         NAME                                STATE     READ WRITE CKSUM
         ost-001                             ONLINE       0     0 0
           raidz2-0                          ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:0:0   ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:1:0   ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:2:0   ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:3:0   ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:4:0   ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:15:0  ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:16:0  ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:17:0  ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:18:0  ONLINE       0     0 0
             pci-0000:08:00.0-scsi-0:2:19:0  ONLINE       0     0 0

errors: No known data errors

Filesystem            Size  Used Avail Use% Mounted on
ost-001/ost0024       5.4T  3.4T  2.0T  64% /mnt/ost-001

> Also, how often are disks failing and how long does a replacement take 
> to resilver, with your current disks?
These are old systems, and the underlying WD 750GB disks are going at an 
average of 1 or 2 per week, with some 270 disks running this way.  Some 
shelves have newer larger disks, and those disks are giving us no 
issues.  We have a number of bigger, newer disk spares that we wanted to 
swap in, giving us more of the 750GB units as spares.

Resilvering typically takes 6hrs or so these days.


> -Olaf
> ------------------------------------------------------------------------
> *From:* Bob Ball [ball at umich.edu]
> *Sent:* Monday, November 23, 2015 12:22 PM
> *To:* Faaland, Olaf P.; Morrone, Chris
> *Cc:* Bob Ball
> *Subject:* Expanding a zfsonlinux OST pool
> Hi,
> We have some zfsonlinux pools in use with Lustre 2.7 that use some 
> older disks, and we are rapidly running out of spares for those.  What 
> we would _like_ to do, if possible, is replace all of those 750GB 
> disks in an OST, one at a time with re-silver between, with 1TB disks, 
> then expand the OST when the last is complete to utilize the larger 
> space and the more reliable disks.
> Is this going to work?  One of us here found the following:
>     According to the Oracle docs, a pool can autoexpand if you set it to
>     do so.  I think the default must be off because the one I checked is
>     off (but that does indicate support of the feature in the linux
>     release also).
>     http://docs.oracle.com/cd/E19253-01/819-5461/githb/index.html
>     [root at umdist02 ~]# zpool get autoexpand ost-006
>     ost-006  autoexpand  off     default
> We are using zfsonlinux version  Can we follow the procedures outlined in the oracle doc using zfsonlinux?
> I guess my initial question assumed the expansion would not happen until the last disk is added and re-silvered, but the document indicates this is not really necessary?
> Thanks,
> bob

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