[DRBD-user] drbdadm verify speed

Ravi Kanth raveeknth at gmail.com
Thu Oct 21 18:01:24 CEST 2010


My machines have 4 processors (Intel Xeon CPU E5430 @ 2.66 Ghz) on each
machine, 4GB RAM and 2.6.18-194.11.4.el5 linux kernel version.

Problem I was trying to solve was syning the data between 3 machines.
Consider we have 3 machined A, B, C. If you sync A-B then disconnect them
and connect B-C then they are synced for the first time. Now If we
disconnect B-C and reconnect A-B and write some data onto the disks, these
data changes are not getting recognised or found when we connect B-C. So
when I do a drbdadm verify I can find the out-of-sync blocks. But this
process seems to be very slow (60Mbps). Is there any other way to find out
of sync blocks on the disks?

Is there any way I could (i mean drbd) write to metadata, changes that are
being made even when the disks are connected as primary/secondary?

If I have 4 processors, will they be all used? Or should I make any changes
to use all of them? Does increasing RAM might have any
increase in performance?

Ravee
On Tue, Oct 19, 2010 at 9:26 PM, J. Ryan Earl <oss at jryanearl.us> wrote:

> On Tue, Oct 19, 2010 at 1:35 PM, Ravi Kanth <raveeknth at gmail.com> wrote:
>
>> I am trying to use drbdadm verify resources and I can only get 60Mbps data
>> rate. I am using infiniband and my syncer rate is 500Mbps.
>>
>
> InfiniBand doesn't matter, you'd get the same verification performance on a
> GigE network as you are CPU limited; single-thread limited to be precise.
>  You need a faster CPU or a dedicated checksum engine such as the CRC32C
> implementation in the newer 32nm Intel processors with a sufficiently new
> revision of the kernel: http://lwn.net/Articles/292984/
>
>  Is there any setting that I can change for the verification to happen at
>> the full bandwidth speed? I want to use the full bandwidth for verification.
>>
>
> You can try different checksum algorithms.  The bandwidth used by the
> checksum verify is a small fraction of the reported checksumming speed.
>  Unfortunately the verify requires a checksumming algorithm at the moment,
> in your case where bandwidth between hosts is gratuitous, it would be more
> efficient to NOT calculate checksums at all and just compare raw data.  To
> my knowledge, DRBD does not support this currently.
>
> -JR
>
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