[Bug 212681] I/O is slow for FreeBSD DOMu on XenServer

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=212681

--- Comment #5 from rainer at ultra-secure.de ---
10.3-RELEASE-p5:

(server </srv>) 0 # time dd if=/dev/zero of=test.dat bs=64k count=20480
20480+0 records in
20480+0 records out
1342177280 bytes transferred in 1.769942 secs (758317078 bytes/sec)
dd if=/dev/zero of=test.dat bs=64k count=20480  0.02s user 1.75s system 99% cpu
1.775 total
(server </srv>) 0 # time dd if=/dev/zero of=test.dat bs=64k count=204800
204800+0 records in
204800+0 records out
13421772800 bytes transferred in 17.266468 secs (777331701 bytes/sec)
dd if=/dev/zero of=test.dat bs=64k count=204800  0.15s user 17.06s system 99%
cpu 17.271 total

This is ZFS.
Probably due to compression on.


root at other-server:/srv# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.4 LTS
Release:        14.04
Codename:       trusty
root at other-server:/srv# time dd if=/dev/zero of=test.dat bs=64k count=20480
20480+0 records in
20480+0 records out
1342177280 bytes (1.3 GB) copied, 2.5559 s, 525 MB/s

real    0m2.571s
user    0m0.041s
sys     0m2.125s

root at other-server:/srv# time dd if=/dev/zero of=test.dat bs=64k count=204800
204800+0 records in
204800+0 records out
13421772800 bytes (13 GB) copied, 93.6892 s, 143 MB/s

real    1m33.940s
user    0m0.219s
sys     0m26.136s


root at yet-another-server:/srv# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.1 LTS
Release:        16.04
Codename:       xenial
root at yet-another-server:/srv# time dd if=/dev/zero of=test.dat bs=64k
count=20480
20480+0 records in
20480+0 records out
1342177280 bytes (1.3 GB, 1.2 GiB) copied, 1.62124 s, 828 MB/s

real    0m1.652s
user    0m0.004s
sys     0m1.616s
root at yet-another-server:/srv# time dd if=/dev/zero of=test.dat bs=64k
count=204800
204800+0 records in
204800+0 records out
13421772800 bytes (13 GB, 12 GiB) copied, 100.348 s, 134 MB/s

real    1m40.711s
user    0m0.172s
sys     0m25.004s


So, in this particular test, it's actually faster.
But I can assure you, in practical use, it's not.


10.3-RELEASE-p7, UFS:

(freebsd-srv2 </srv>) 0 # time dd if=/dev/zero of=test.dat bs=64k count=20480
20480+0 records in
20480+0 records out
1342177280 bytes transferred in 8.746548 secs (153452229 bytes/sec)
dd if=/dev/zero of=test.dat bs=64k count=20480  0.02s user 1.65s system 19% cpu
8.756 total
(freebsd-srv2 </srv>) 0 # time dd if=/dev/zero of=test.dat bs=64k count=204800
204800+0 records in
204800+0 records out
13421772800 bytes transferred in 99.078364 secs (135466233 bytes/sec)
dd if=/dev/zero of=test.dat bs=64k count=204800  0.22s user 18.20s system 18%
cpu 1:39.30 total

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