ZFS UNMAP performance

[Danny Schales]

I'm seeing very slow performance with certain operations on a ZFS
filesystem built on ISCSI LUN's on a 10.0 system (new ISCSI
implementation).  The issue appears to be with BIO_DELETE operations.
Monitoring the system with gstat shows expected times for read and write
operations, but deletes are in the multiple hundreds of milliseconds
under normal operation.  Destroying a snapshot sends the times to
astronomical levels.  sysctl says the system is using UNMAP for deletes:

kern.cam.da.0.delete_method: UNMAP

I searched and found where Oracle issued a performance alert for Solaris
11.1 where ZFS using UNMAP was in use.  Here's a link to a blog
discussing it:

http://schalwad.blogspot.com/2013/12/solaris-111-zfs-write-performance.html


Is FreeBSD also impacted?  If so, is there a fix or a workaround?

Thanks

Danny Schales

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 196 bytes
Desc: OpenPGP digital signature
URL: <http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20140311/0f89dfe6/attachment.sig>