On 03/05/2011 20:25, John wrote:
What I do is to cat the 330MB binary file (XP service pack from Microsoft) 20 times into
a single 6.6GB file, "date" before and afterwards, and after the second date
finishes, immediately Force power shut down. There are two observations:
1. the time to complete copying into this 6.6GB file were 72s, 44s, 79s in
three runs, presumably because there is another production VM on the same host.
The average is 65s, so it's about 100MB/s.
2. After immediately power down, I do found the resulting file was less than
6.6GB. So indeed the VM claimed the completion of the copying before it
actually did.
I then did the same thing on the virtualbox, since I don't want the above premature I/O,
I made sure the "Use Host I/O cache" is unchecked for the VM storage.
1. the time to complete copying into this 6.6GB file was 119s and 92s, the
average is 105s, so the speed is 62MB/s.
2. after immediately "Reset" the machine, I couldn't boot. Both times it asked
me to do fsck for that partition (GPT 2.2T). But after finally powering up, I found the
file was also less than 6.6GB both times as well.
So looks like virtualbox also suffers caching problem? Or did I do anything
wrong?
Aaargh. Please don't invent benchmarks. The ones which are already
around have enough troubles by themselves.
Instead, if you really want to do a proper comparison of the systems, do
this (in the order I've written):
1) add these lines to /etc/sysctl.conf:
vfs.hirunningspace=8388608
vfs.lorunningspace=6291456
vfs.read_max=128
2) configure the FreeBSD system to use AHCI
http://ivoras.net/blog/tree/2009-11-17.trying-ahci-in-8.0.html
3) use benchmarks/bonnie++ from ports for benchmarking. Note that you
need to run *the same version of the benchmark* on all systems (i.e.
also on Linux) to be able do do comparison.
Any do-it-yourself benchmarks you do are very likely meaningless and you
cannot conclude anything from them. Even with this, there could be
*huge* differences in the results simply as a consequence of rotational
positions of virtual drives on the physical one. See this results (note
the transfer rate results).
lara:~# diskinfo -vt /dev/ada0
/dev/ada0
512 # sectorsize
500107862016 # mediasize in bytes (466G)
976773168 # mediasize in sectors
0 # stripesize
0 # stripeoffset
969021 # Cylinders according to firmware.
16 # Heads according to firmware.
63 # Sectors according to firmware.
6QG3Z026 # Disk ident.
Seek times:
Full stroke: 250 iter in 5.671675 sec = 22.687 msec
Half stroke: 250 iter in 4.294470 sec = 17.178 msec
Quarter stroke: 500 iter in 6.793844 sec = 13.588 msec
Short forward: 400 iter in 2.637252 sec = 6.593 msec
Short backward: 400 iter in 2.320116 sec = 5.800 msec
Seq outer: 2048 iter in 0.217796 sec = 0.106 msec
Seq inner: 2048 iter in 0.218317 sec = 0.107 msec
Transfer rates:
outside: 102400 kbytes in 1.221390 sec = 83839 kbytes/sec
middle: 102400 kbytes in 1.445180 sec = 70856 kbytes/sec
inside: 102400 kbytes in 2.451970 sec = 41762 kbytes/sec
Benchmarking file systems and drive IO is complicated :)
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