[DRBD-user] Latency problems with DRBD 0.8.4 and a 3ware RAID5

[Igor Neves]

Hi,

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.

Cheers,

On 31-08-2011 12:46, Florian Apolloner wrote:
> Hi,
>
> 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
> too.
>
> 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
>
>
>
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> drbd-user at lists.linbit.com
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-- 
Igor Neves<igor.neves at 3gnt.net>
3GNTW - Tecnologias de Informação, Lda

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