On Mon, 28 Sep 2009, Bob Friesenhahn wrote:
This should work but it does not verify the redundant metadata. For example,
the duplicate metadata copy might be corrupt but the problem is not detected
since it did not happen to be used.
I am finding that your tar incantation is reading hardly any data from
disk when testing my home directory and the 'tar' happens to be GNU
tar:
# time tar cf - . > /dev/null
tar cf - . > /dev/null 2.72s user 12.43s system 96% cpu 15.721 total
# du -sh .
82G
Looks like the GNU folks slipped in a small performance "enhancement"
if the output is to /dev/null.
Make sure to use /bin/tar, which seems to actually read the data.
When actually reading the data via tar, read performance is very poor.
Hopefully I will have a ZFS IDR to test with in the next few days
which fixes the prefetch bug.
Zpool scrub reads the data at 360MB/second but this tar method is only
reading at an average of 6MB/second to 42MB/second (according to zpool
iostat). Wups, I just saw a one-minute average of 105MB and then
131MB. Quite variable.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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