I ran some more tests with dd to create a 2Gb file, here is the output:
server:share # time dd if=/dev/zero of=test_dd count=16k bs=128k
0
16384+0 poster i
16384+0 poster ut
dd if=/dev/zero of=test_dd count=16k bs=128k 0,02s user 1,76s system 32% cpu
5,414 total
server:share # time dd if=/dev/zero of=test_dd count=32k bs=64k
0
32768+0 poster i
32768+0 poster ut
dd if=/dev/zero of=test_dd count=32k bs=64k 0,03s user 3,52s system 71% cpu
4,979 total
server:share # time dd if=/dev/zero of=test_dd count=64k bs=32k
0
65536+0 poster i
65536+0 poster ut
dd if=/dev/zero of=test_dd count=64k bs=32k 0,04s user 3,62s system 71% cpu
5,109 total
server:share # time dd if=/dev/zero of=test_dd count=128k bs=16k
0
131072+0 poster i
131072+0 poster ut
dd if=/dev/zero of=test_dd count=128k bs=16k 0,07s user 3,98s system 73% cpu
5,503 total
server:share # time dd if=/dev/zero of=test_dd count=512k bs=4k
0
524288+0 poster i
524288+0 poster ut
dd if=/dev/zero of=test_dd count=512k bs=4k 0,27s user 6,78s system 82% cpu
8,563 total
server:share # time dd if=/dev/zero of=test_dd count=1024k bs=2k
0
1048576+0 poster i
1048576+0 poster ut
dd if=/dev/zero of=test_dd count=1024k bs=2k 0,53s user 10,64s system 87% cpu
12,816 total
server:share # time dd if=/dev/zero of=test_dd count=2048k bs=1k
0
2097152+0 poster i
2097152+0 poster ut
dd if=/dev/zero of=test_dd count=2048k bs=1k 1,07s user 18,38s system 91% cpu
21,353 total
I understand that for smaller files, and hence smaller stripes, raidz
performance suffers. The home directory I backed up recently over NFS (3.4Gb
total) took quite some time (didn't measure then). But the average file size
seems to be 83k for the directory, according to
# find /home/olale -type f -exec ls -l '{}' \; | awk '{total += $5} END {
print total / NR }'
so files aren't *that* small..
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