Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Maurice Volaski wrote:
> Thank you for your detailed response.
>
You are welcome.
>> Maurice Volaski wrote:
>>
<SNIP>
>>
>>
>> Q1: you did not mention, Is DRBD transferring over a dedicated network
>> cable or the one shared with the rest of your LAN? For my test setup
>> I have it shared with the LAN and get some variance, but I think the
>> network switch prevents me from being hit as hard as you, i.e., on
>> 100Mb connection I am seeing ~8500K/sec +-500K/sec.
>
>
> Our network should be operating at wire speed, which for the "slow"
> pair, is full-duplex 100BaseT. The fast pair is dual, full-duplex
> gigabit on the primary (using adaptive load-balancing) and single
> full-duplex gigabit on the other.
>
>> Q2: how hard can you drive the hard drives (on both systems) without
>> DRBD?
>> on my systems `dd if=/dev/zero of=/dev/hda13 bs=4k` has `iostat -x
>> /dev/hda 2` showing ~30000kB/s on both systems. With DRBD, proto C,
>> `dd if=/dev/zero of=/drbd0mnt/testzone/junk bs=4k` gets an iostat of
>> ~8300KB/s.
>
>
> iostat gives me bogus values. For example, on the non-DRBD disk, it's
> 28.49 rkB/s, which, if I understand correctly means 28.49 KB/second, and
> that's obviously bogus.
>
For the way I wrote the test it is the wkB/s you want to watch.
Also `iostat -x /dev/hda 10` would give a little easier to read averaging, and
I am assuming the other partitions on hda are quiet.
> Using time with dd, I found the DRBD disk to be about 13 MB/second and
> the non-DRBD disk to be 29 MB/second on the slow set of servers.
This was with them connected and DRBD up on both?
If so that sounds good considering your network speed.
>
> On the fast servers, the non-DRBD disk tested via dd yields an
> astounding 182 MB/second and the DRBD disk, a mere 16 MB/second.
>
> Actually, that's in line with drbd.conf. So I want to make clear that I
> have seen these slow numbers only when the secondary has been offline
> for some time and there is quite a bit of data to be resynced.
So you are saying that with the pair completely synced, if you run the same
tests you get much better numbers (which would only be logical), or are you
saying that with the unit under test disconnected from it's mate and having a
lot of data out of sync, the numbers drop while they are still disconnected?
<SNIP>
>
> On the slow server pair:
> ttcp-t: 134217728 bytes in 28.13 real seconds = 4659.27 KB/sec +++
> ttcp-t: 16384 I/O calls, msec/call = 1.76, calls/sec = 582.41
>
This is on 100Mb/s ethernet???
is drbd (or something else) also using the network at that time?
i.e., this seems really slow.
For a two computer 100Mb/s ethernet with nothing else on it, the theoretical
limit is ~12000KB/sec, most times you can practically see 11000KB/sec, and you
are only seeing ~1/3 the theoretical...
> I wonder if the fact that the secondary of the slow pair's having only
> 256 MB impacts the overall performance for this result.
Should not really be a problem unless you are running x, gnome/kde, firefox,
thunderbird, OpenOffice.org, and emacs {:^) all at the same time.
>
> On the fast server pair:
> ttcp-t: 134217728 bytes in 1.88 real seconds = 69817.52 KB/sec +++
> ttcp-t: 16384 I/O calls, msec/call = 0.12, calls/sec = 8727.19
<SNIP>
That looks good to go from here.