gmirror

[Vladimir Dzhivsanoff]

On 5/14/05, Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
> On Sat, May 14, 2005 at 01:22:05PM +0400, vohand at gmail.com wrote:
> +> 
> +> Hardware: SATA RAID adapter with SiliconImage 3114 chip. 2 SATA HDD.
> +> I did gmirror.
> +> 
> +> Run test:
> +> 3 parallel tasks "dd if=/dev/mirror/gm0 of=/dev/null bs=1m count=5000"
> +> 
> +> gstat shows summary read speed from mirror about 30-40 mbyte/sec.
> +> It is for all balance algorithms: load, round-robin, split
> +> 
> +> While, one "dd if=/dev/ad4 of=/dev/null bs=1m count=5000" shows 50
> mbyte/sec
> +> 
> +> 1. Why it occurs and how fix it ?
> +> 
> +> 2. If in the test instead of three instancies of "dd if=/dev/mirror/gm0
> +> of=/dev/null bs=1m count=5000" run only one, 
> +>    then read speed don`t exceeds read speed from one disk (dd
> if=/dev/ad4
> +> of=/dev/null bs=1m count=5000)
> +> 	a) This is gmirror feature ?
> +> 	b) This is hardware feature (SiliconImage 3114 chip) ?
> 
> This is the way RAID1 works. Try to imagine how disk's heads are moving -
> there will be no speed-up in sequential reads, this is not RAID0.
> 
> Mirror characteristics are:
> - the same speed for sequential reads as for one disk;
> - the same speed for sequential/random write as for one disk;

========================================================
> - double speed of one disk for random reads;

by what test-suite I can test it ?
and what balance algorithm is more proper for random reads ?

three parallel tasks of "dd ...." is not good model for random reads ?

> 
> -- 
> Pawel Jakub Dawidek                       http://www.wheel.pl
> pjd at FreeBSD.org                           http://www.FreeBSD.org
> FreeBSD committer                         Am I Evil? Yes, I Am!
> 
>