Dne 20.9.2014 v 16:19 lilofile napsal(a):
when I test Thinly-Provisioned Logical Volumes(use device thinprovison target),I found the random write performance is very low. What factors will influence the random write performance of thin volume. how can i quickly understand dm-bufio.c?
In general 2 major factors -
1. - size of chunk/(provisioned block)
the bigger the block is - the better usually filesystem performs - since the
all the aggregation logic and optimization of fs works.
on the other - the bigger the block is - the less efficient snapshot you get
(since much bigger chunk needs to be copied for i.e. single byte write)
2. - zeroing on provisionsing.
when the block provisioned for the first time - it's (by default config) fully
zeroes - so you don't get random disk content from unwritten areas.
If you don't care about this - you could safely disable zeroing - number of
filesystem usually already manages unwritten space well so if you use block
device for ext4 so shouldn't normally be able to read unwritten areas.
So please try i.e. 256KB chunk size with non-zeroing (-c 256 -Zn) when
creating thin-pool - do you still fell you get poor performance ?
Zdenek
NOTE: you could change zeroing with existing pool, but not your thin-pool
chunk size for now (though future version might be less restrictive here).
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
