To some extent it already does.
If what you're talking about is filesystems/datasets, then all
filesystems within a pool share the same free space, which is
functionally very similar to each filesystem within the pool being
thin-provisioned. To get a "thick" filesystem, you'd need to set at
least the filesystem's reservation, and probably quota as well.
Basically filesystems within a pool are thin by default, with the added
bonus that space freed within a single filesystem is available for use
in any other filesystem within the pool.
If you're talking about volumes provisioned from a pool, then volumes
can be provisioned as "sparse", which is pretty much the same thing.
And if you happen to be providing ISCSI luns from files rather than
volumes, then those files can be created sparse as well.
Reclaiming space from sparse volumes and files is not so easy unfortunately!
If you're talking about the pool itself being thin... that's harder to
do, although if you really needed it I guess if you provision your pool
from an array that itself provides thin provisioning.
Regards,
Tristan
On 30/12/2009 9:34 PM, Andras Spitzer wrote:
Hi,
Does anyone heard about having any plans to support thin devices by ZFS? I'm
talking about the thin device feature by SAN frames (EMC, HDS) which provides
more efficient space utilization. The concept is similar to ZFS with the pool
and datasets, though the pool in this case is in the SAN frame itself, so the
pool can be shared among different systems attached to the same SAN frame.
This topic is really complex but I'm sure it's inevitable to support for
enterprise customers with SAN storage, basically it brings the differentiation
of space used vs space allocated, which can be a huge difference in a large
environment, and this difference is major even on the financial level as well.
Veritas already added support to thin devices, first of all support to VxFS to be
"thin-aware" (for example how to handle over-subscribed thin devices), then
Veritas added a feature called SmartMove, a nice feature to migrate from fat to thin
devices, and the most brilliant feature of all (my personal opinion, of course) is they
released the Veritas Thin Device Reclamation API, which provides an interface to the SAN
frame to report unused space at the block level.
This API is a major hit, and even though SAN vendors today doesn't support it,
HP and HDS already working on it, and I assume EMC has to follow as well. With
this API Veritas can keep track of files deleted for example, and with a simple
command once a day (depending on your policy) it can report the unused space
back to the frame, so thin devices [b]remain[/b] thin.
I really believe that ZFS should have support to thin devices, especially
referring to the feature what this API brings into this field, as it can result
a huge cost difference to enterprise customers.
Regards,
sendai
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