[DRBD-user] Extremely high latency problem

Philipp Marek philipp.marek at linbit.com
Thu Jun 5 12:34:45 CEST 2014

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Hi Bret,

> Intel(R) Xeon(R) CPU E3-1230 V2 @ 3.30GH
> CentoS 6.5 - 2.6.32-431.17.1.el6.x86_64
> drbd version: 8.3.16 (api:88/proto:86-97)
please use 8.4.4 (or .5).
Eg because of http://blogs.linbit.com/p/469/843-random-writes-faster/

> dd if=/dev/zero of=./testbin  bs=512 count=1000 oflag=direct
> 512000 bytes (512 kB) copied, 32.3254 s, 15.8 kB/s
This means ~32msec per write.

But: you're writing into a _filesystem_, not directly onto the DRBD 
And that means quite some write amplification - each 512 byte write 
_might_ result (depending on the filesystem) in _multiple_ write-
requests, each with a separate barrier ...

Please try writing into a DRBD device, without any filesystem inbetween; 
and using 4kB blocks might help to avoid read/modify/write cycles, too.

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