[illumos-Developer] Review --> iSCSI UNMAP support

[Bill Sommerfeld]

On 02/10/11 08:22, Sumit Gupta wrote:
> UNMAP-101: If I unmap 1G space then 1G of extra space is available for other zvols. If you are not doing that, then your implementation is wrong.

eric is correct and you are wrong.

reservations in practice can be a hard concept to wrap your brain around 
-- particularly the interaction between snapshots, refreservations, and 
pool free space.

if your actual allocated space is equal to your reservation, and you 
free 1G of space, the pool will ensure that you will be able to use 
another 1G of space -- if everyone else goes nuts writing until the pool 
stops them, but you don't use any more space, the pool will keep 1G in 
reserve for you.

in the mean time, the pool has 1G more room to play with under the 
covers, which may reduce the amount of fragmentation that all users of 
the pool may suffer from and generally improve performance.

And it also reduces the size of any snapshots you create from the zvol.

						- Bill