Hi,
I have an application that creates some 228 thousand files,
spread over about 4000 directories. Total is not more than
1.3Gb. (I'm not sure, and I don't care if it's 10% or 90% of
that number)
Anyway, I've loaded all of the 1.3Gb into the cache (the machine
has 8Gb of RAM), so that only writes need to take place.
After a while the machine goes into a routine of writing
about 500 to 1000kbytes per second.
Sync seems to take a long time:
zebigbos:/recover7/bd4256_jense/tree> time sync
0.004u 0.136s 5:44.66 0.0% 0+0k 0+0io 0pf+0w
zebigbos:/recover7/bd4256_jense/tree>
The machine normally reads up to about 150 Mbytes per second without
trouble.
I'm suspecting that the writes to the inodes and files all end
up "fragmented" such that reads to complete the RAID stripes
need to be performed:
Iostat shows:
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 75.25 277.23 126.73 280 128
sdb 91.09 400.00 134.65 404 136
sdc 71.29 253.47 95.05 256 96
sdd 100.99 221.78 304.95 224 308
However, I would say that all those new files should be "clustered"
such that the chances of writing a full stripe becomes reasonable.
Moreover, clustering should, even with reading other parts of the
stripe result in a performance on the order of 10 to 50 times better.
Raid block (stripe) size is 64k. (Next time I format a partition,
I will chose 512k, causing the readperformance to increasae from 150Mb
per second to about 200Mb per second).
Roger.
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