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From: Nikolay Denev <ndenev@gmail.com>
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Date: Wed, 25 Jan 2012 09:51:04 +0200
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Subject: BIO_DELETE support for ZVOLs?
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I'm don't know if anyone thought about this but it seems like a
nice feature to support TRIM like functionality for ZVOLs.

For example : if there is a sparse ZFS volume, formatted with UFS,
and you fill it up once, then the disk space used will be with the size =
of the ZVOL.
Then even if there is freed space on the UFS filesystem,
the ZVOL disk space allocated from the ZVOL will remain the same.

This also will be very nice if can be supported for FC exported ZVOLs =
via the new CAM Target Layer.