2011-09-20 04:38 PM
when i create a volume in a aggr. there is always 20% reserved for snapshots.
then afterwards I remove it
snap reserve -v vol_name 0
Is this set on the aggr level or I have to turn it off manually per volume?
aggr options my_aggr shows:
nosnap=off, raidtype=raid_dp, raidsize=16, ignore_inconsistent=off,
snapmirrored=off, resyncsnaptime=60, fs_size_fixed=off,
snapshot_autodelete=on, lost_write_protect=on, ha_policy=cfo
Is it bad to remove this 20% reservation?
2011-09-20 06:20 PM
The root volume is used as the default for new volumes. "vol status" to see which volume is root. That volume has the 20% reserve and is used for new volumes. Most don't want 0% for root so need to modify new volumes after creation to have a different %.
2011-09-21 01:21 AM
It is not bad to set the snap reserve to 0%. It depends how you want to manage the space within the volume. I always set it to 0% for volumes with LUNs and NFS Datastores and SnapVault Destination data.
You are right, there is a snap reserve on the aggregate as well. Be careful, when setting this to 0% you also "disable" the snapshots on aggregate level (because of snapshot autodelete)... And if you want to mirror the aggregate (with local_syncmirror) then you need the aggr snap reserve to be set to at least 5%. I very rarely change this to 0%.
Hope this helps,
2011-09-21 03:10 AM
The 8.1 default for the root aggregate will be 0% aggr reserve and I think the default for other aggrs will be 3 or 5% still (we'll know for sure when released hopefully at the end of the month).
I don't like leaving it at zero either and had one case where we were able to aggr copy -s to copy a specific aggr snap to get a volume back that was deleted accidently at a customer. I really wish we had "snap reserve -A -t file" to restore a flexvol as a single fle restore at the aggr level since it is an aggr object but that doesn't work today... aggr copy -s is a workaround but requires enough space and a full copy of that snap to get a volume back...but is a good use case on what we can do with aggr snaps even without syncmirror.