On Wed, 11 Nov 2009, Darren J Moffat wrote:
Zfs is absolutely useless for this if the underlying storage uses
copy-on-write. Therefore, it is absolutely useless to put it in
zfs. No one should even consider it.
I disagree. Sure there are cases where ZFS which is copy-on-write
is sitting ontop of something that is copy-on-write (iSCSI luns
backed by ZFS on another system for example) that doesn't mean there
are no cases where this is useful. For example in an appliance or
other controlled environment it isn't useless and it is being
considered for example those use cases of ZFS.
Perhaps in a product where the engineering team has examined every
part of the product from top to bottom, it might have some use.
Advertising that the feature exists might cause someone to believe
that it actually works. There are plenty of devices in common use
which are always/sometimes COW. These include SSDs and certain types
of CD/DVD/WORM drives. For SSDs, COW is commonly called "wear
leveling". In hard-drives, we have what is known as "bad block
management".
Given that many storage products are made in places in China, it seems
unlikely that any government is going to trust assurances from a
product vendor that their product never leaves behind copies of data.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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