I'm just trying the delaylog mount option on a filesystem (LVM over
2x 2TB 4K sector drives), and I see this while running 8 processes
of "rm -r * & 2>/dev/null":
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz
avgqu-sz await svctm %util
sdc 2,80 33,40 125,00 64,60 720,00 939,30 17,50
0,55 2,91 1,71 32,40
sdd 0,00 25,60 122,80 63,40 662,40 874,40 16,51
0,52 2,77 1,96 36,54
dm-0 0,00 0,00 250,60 123,00 1382,40 1941,70 17,79
1,64 4,39 1,74 65,08
Then I issue "sync", and utilisation increases:
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz
avgqu-sz await svctm %util
sdc 0,00 0,20 15,80 175,40 84,00 2093,30 22,78
0,62 3,26 2,93 55,94
sdd 0,00 1,00 13,40 177,60 79,20 2114,10 22,97
0,69 3,63 3,34 63,80
dm-0 0,00 0,00 29,20 101,20 163,20 4207,40 67,03
1,11 8,51 7,56 98,60
This is reproducible. Now it can be that the sync just causes more writes and
stalls reads
so overall it's slower, but I'm wondering why none of the devices says "100%
util", which
should be the case on deletes? Or is this again the "mistake" of the
utilization calculation
that writes do not really show up there?
I know I should have benchmarked and tested, I just wanted to raise eyes on
this as it
could be possible there's something to optimize.
Another strange thing: After the 8 "rm -r" finished, there were some subdirs
left over
that hadn't been deleted - running one "rm -r" cleaned them out then. Could
that be
a problem with "delaylog"? Or can that happen when several "rm" compete in the
same
dirs?
This is kernel 2.6.35.4
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