Richard,
thanks for the heads-up. I found some material here that sheds a bit
more light on it:
http://en.wikipedia.org/wiki/ZFS
http://all-unix.blogspot.com/2007/04/transaction-file-system-and-cow.html
Regards,
heinz
Richard Elling wrote:
On Feb 15, 2010, at 8:43 PM, heinz zerbes wrote:
Gents,
We want to understand the mechanism of zfs a bit better.
Q: what is the design/algorithm of zfs in terms of reclaiming unused blocks?
Q: what criteria is there for zfs to start reclaiming blocks
The answer to these questions is too big for an email. Think of
ZFS as a very dynamic system with many different factors influencing
block allocation.
Issue at hand is an LDOM or zone running in a virtual (thin-provisioned) disk
on a NFS server and a zpool inside that vdisk.
This vdisk tends to grow in size even if the user writes and deletes a file
again. Question is, whether this reclaiming of unused blocks can kick in
earlier, so that the filesystem doesn't grow much more than what is actually
allocated?
ZFS is a COW file system, which partly explains what you are seeing.
Snapshots, deduplication, and the ZIL complicate the picture.
-- richard
ZFS storage and performance consulting at http://www.RichardElling.com
ZFS training on deduplication, NexentaStor, and NAS performance
http://nexenta-atlanta.eventbrite.com (March 15-17, 2010)
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