Ok, Phil.
I ran some tests on our (crappy) RAID0, comprised of two 300GB SAS
drives. Here's what I got for varying block sizes:
DRBD connected:
8K - 26MB/s
16K - 39MB/s
32K - 65MB/s
64K - 92MB/s
128K - 121MB/s
256K - 137MB/s
512K - 152MB/s
1M - 177MB/s
2M - 196MB/s
4M - 197MB/s
DRBD disconnected:
8K - 57MB/s
16K - 95MB/s
32K - 144MB/s
64K - 196MB/s
128K - 242MB/s
256K - 272MB/s
512K - 285MB/s
1M - 292MB/s
2M - 297MB/s
4M - 287MB/s
Those disconnected numbers look not too far off from raw disk
performance in a simple 2-disk RAID0. To be fair, this is with DRBD
8.4.1, and with the following disk options:
disk {
disk-barrier no;
disk-flushes no;
md-flushes no;
}
And we could do all that because we have capacitor-backed RAID controllers.
We're seeing pretty much *exactly* what you should expect. This is with
the 3.2.0 kernel as well. To make sure this wasn't fake, I monitored
iostat and watched Dirty and Writeback from /proc/sys/meminfo. These are
legit numbers obtained directly from dd and oflag=sync for all tests.
So, I'm not sure about your own setup, but I can confirm that DRBD does
honor sync in our case.
--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
stho...@optionshouse.com
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