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List:       drbd-user
Subject:    Re: [DRBD-user] Writes are much too slow
From:       Florent DUTHEIL <florent.dutheil-renexter () renault ! com>
Date:       2008-09-25 8:36:34
Message-ID: 48DB4D92.5040104 () renault ! com
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Trent Lloyd a écrit :
> I am in no way surprised by these results.  First note that you are 
> writing out 4K blocks, then forcing a sync.  So you can see already 
> this is a slow operation from the non-DRBD results.  As each time you 
> write 4k you need to wait for it to sync before it can do the next 4k.
> 
> Problem with doing a force sync on DRBD is you introduce network 
> latency into the 'sync' pipeline.. so it writes 4K.. sends a sync and 
> you have to wait for that to go over the network, get synced, and come 
> back, before it can move onto the next 4k block.
A simple bonnie++ session would allow to compare "putc()" and 
"intelligent" writes performance (same with reads). It's not a "real 
world" benchmark though.

Artur, you mentioned drbd fine tuning, but check your hosts network 
settings too (MTU especially).


Florent


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