> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Edward Ned Harvey
>
> --- Performance loss:
I ran one more test, that is rather enlightening. I repeated test #2 (tweak
arc_meta_limit, use the default primarycache=all) but this time I wrote 100%
duplicate data instead of unique. Dedup=sha256 (no verify). Ideally, you
would expect this to write very very fast... Because it's all duplicate
data, and it's all async, the system should just buffer a bunch of tiny
metadata changes, aggregate them, and occasionally write a single serial
block when it flushes the TXG. It should be much faster to write dedup.
The results are: With dedup, it writes several times slower. Just the same
as test #2, minus the amount of time it takes to write the actual data. For
example, here's one datapoint, which is representative of the whole test:
time to write unique data without dedup: 7.090 sec
time to write unique data with dedup: 47.379 sec
time to write duplic data without dedup: 7.016 sec
time to write duplic data with dedup: 39.852 sec
This clearly breaks it down:
7 sec to write the actual data
40 sec overhead caused by dedup
<1 sec is about how fast it should have been writing duplicated data
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
