[OpenIndiana-discuss] rpool defragmentation

[Jim Klimov]

On 16 January 2015 16:22:15 CET, Andrew Gabriel <illumos at cucumber.demon.co.uk> wrote:
>On 01/16/15 02:37 PM, Gary Gendel wrote:
>> # zpool list
>> NAME      SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP HEALTH 
>> ALTROOT
>> rpool      68G  49.5G  18.5G         -    50%    72%  1.00x ONLINE -
>> users     928G  72.4G   856G         -     1%     7%  1.00x ONLINE -
>>
>> # zfs list
>> NAME                    USED  AVAIL  REFER  MOUNTPOINT
>> rpool                  48.9G  16.9G    82K  /rpool
>> rpool/ROOT             44.9G  16.9G    22K  legacy
>> rpool/ROOT/hipster-17  44.9G  16.9G  34.9G  /
>> rpool/dump             1.97G  16.9G  1.97G  -
>> rpool/export             32K  16.9G    32K  /export
>> rpool/swap             2.01G  16.9G  2.01G  -
>> users                  72.4G   827G  72.3G  /export/home
>>
>> How does one defragment this?
>
>I presume you are referring to rpool, and not users?
>
>What makes you think you need to?
>What do you use the root filesystem for?
>
>> I thought about creating a new BE and then sending the current BE to 
>> it, but there doesn't seem to be enough room.
>
>Since rpool can only be either a single disk or a mirror, the easiest 
>way to defrag it is to attach another mirror side and let it resilver. 
>The new mirror side will be defragged. Make sure the new disk is 
>bootable (has grub etc on it), and then zpool split off the old disk.
>It 
>would be a good opportunity to move to a bigger rpool disk too.

Are you sure about defragging via mirroring? I believe (from practice digging with on-disk allocation) that offsets in vdev's that comprise a mirror are the same for copies of the same block, as well as raidzN offset into the logical tlvdev divided by total number of disks would give the offset into each disk's part of the vdev to find the sector pertaining to that stripe, and remainder from such division would give the disk number formthe particular byte offset. My description may be a bit blurry so late in the night, but you get the point ;)


Jim
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