[DRBD-user] Latency problems with DRBD 0.8.4 and a 3ware RAID5
igor at 3gnt.net
Thu Sep 1 18:57:10 CEST 2011
Why people keep using bad hardware after million posts on the ML
reporting bad results?
Please, before using some RAID card, do a quick search on the mailing
lists and learn with other mistakes instead of doing the same mistakes. :-)
3ware cards are bad piece of crap. Use other cards, like Areca.
On 31-08-2011 12:46, Florian Apolloner wrote:
> I am having a horrible latency with the following configuration:
> * protocol c
> * raid5 over a 3Ware 9750-4i SAS2 raid controller
> * Dedicated Gigabit link between the two machines, no switch in between.
> This is what I can tell you:
> * iperf shows around 950 Mbits/sec -- sounds okay for gigabit ;)
> * throughput for the drbd raid has 70-80 MByte/sec -- sounds good to me
> Now on to the latency tests (backing device):
> dd if=/dev/zero of=/dev/sda3 bs=512 count=1000 oflag=direct
> 512000 bytes (512 kB) copied, 0.0365779 seconds, 14.0 MB/s
> and onto the drbd device:
> dd if=/dev/zero of=/dev/drbd1 bs=512 count=1000 oflag=direct
> 512000 bytes (512 kB) copied, 9.651 seconds, 53.1 kB/s
> Sounded awfully slow to me, so I compared with a ramdisk:
> dd if=/dev/zero of=/dev/drbd2 bs=512 count=1000 oflag=direct
> 512000 bytes (512 kB) copied, 0.166689 seconds, 3.1 MB/s
> Sounds waaaay better, though I can't tell if that's slow or fast enough.
> The RTT for the link is:
> rtt min/avg/max/mdev = 0.096/0.166/0.207/0.043 ms
> So let's summarize:
> -> Harddisk speed shouldn't be a problem (0.0365779 seconds for the write)
> -> Network speed should be a problem as indicated by RTT and iperf
> -> Network and Harddisk combined -> problems.
> Any hints on how to debug that? I am currently grasping any straw I can
> get :/
> Thx in advance and regards,
> Florian Apolloner
> drbd-user mailing list
> drbd-user at lists.linbit.com
Igor Neves<igor.neves at 3gnt.net>
3GNTW - Tecnologias de Informação, Lda
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