writes. How fast is the array in practice?Thats allways a good question.. This is by far not being the only user
of the array at the time of testing.. (there are 4 FC-channel connected to a
switch). Creating a fresh slice.. and just dd'ing onto it from /dev/zero
gives:
jk@hest:~$ sudo dd if=/dev/zero of=/dev/sdh bs=1M count=10000
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 78.0557 s, 134 MB/s
jk@hest:~$ sudo dd if=/dev/zero of=/dev/sdh bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 8.11019 s, 129 MB/s
Watching using dstat while dd'ing it peaks at 220M/s
Hmm, not as fast as I expected.
It has 2GB of battery backed cache. I'm fairly sure that when it was new
(and I only had connected one host) I could get it up at around 350MB/s.
With 2GB of BBC, I'm surprised you are seeing as much latency as you
are. It should be able to suck down writes as fast as you can throw
at it. Is the array configured in writeback mode?
On a 32GB system that's 1.6GB of dirty data, but your array should beThats another thing. I havent been debugging while hitting it (yet) but if I
able to write that out fairly quickly (in a couple seconds) as long as
it's not too random. If it's spread all over the disk, write
throughput will drop significantly - how fast is data being written to
disk when your system suffers from large write latency?
go ind and do a sync on the system manually. Then it doesn't get above
50MB/s in writeout (measured using dstat). But even that doesn't sum up to 8
minutes .. 1.6GB at 50MB/s ..=> 32 s.
Have you also tried increasing the IO priority of the kjournald
processes as a workaround as Arjan van de Ven suggests?