From owner-freebsd-fs@FreeBSD.ORG  Tue Jun 14 07:19:37 2011
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From: Per von Zweigbergk <pvz@itassistans.se>
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Date: Tue, 14 Jun 2011 09:19:32 +0200
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Subject: Disk usage and ZFS deduplication
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I've been following the "Impossible compression ratio on ZFS" thread =
with some interest, and it made me ask myself this:

Let us say we have a hypothetical zfs filesystem with the equally =
hypothetical files A and B. The filesystem has deduplication enabled. =
Both files have an apparent file size of 100 MB, but 50 MB of that data =
is common between the two files and thus can be deduplicated. This would =
mean that total disk usage would be 150 MB.

If you use "du" to determine disk size for a deduplication, what would =
be the result? Which file would the common data be accounted to? Or =
would it be accounted to both files somehow, in part or in full?=