writes will be the speed of slowest mirror (ssd or hd)
read can have speed improvement with this patch
there´s some options
/sys/block/md0/md/read_balance_mode
near_head = today implementation
round_robin => could be usefull if you have ssd only, since
round_robin consider that access time is the same for any drive (hard
disk access time is diferent for random and sequencial)
stripe => i didn´t get good benchmarks, but it´s nice to have it,
since we could put it over network, some sectors on one disk others on
another (nbd)
time_based => here you should send me some information about you disk
for example:
access time of mirrors (check your drive information website, ssd
are normaly <0.1ms, hard disks near 10~20 ms)
sequencial read speed (use dd if=/dev/sda of=/dev/zero bs=4096,
change the block size to size you will use with your filesystem, for
vertex2 ssd i´m using bs=4096, for disks it´s a good value too, since
disks bs ~= number of heads (2,4,8) )
send me the access time and sequencial read speed and i make the
values to tune your sysfs (/sys/block/md0/md/read_balance_config)
you will need to :
echo "time_based" > /sys/block/md0/md/read_balance_mode
echo "disks informations" > /sys/block/md0/md/read_balance_config
for each mirror, you can´t use sysfs file to configure it, maybe a
bash script is a better solution to configure it, on future version i
will change it and put at /sys/block/md0/md/dev-xxxx/
2011/2/15 Andras Korn <korn@xxxxxxxxxxxxxxxxxxxxxxx>:
> On Tue, Feb 15, 2011 at 06:10:17AM -0300, Roberto Spadim wrote:
>
>> andras could you make some benchmarks to raid1 with round robin read balance?
>> at this site:
>> www.spadim.com.br/raid1/
>>
>> it's kernel 2.6.37 based
>
> Yes, I can do that. Can you give me some hints on what specific
> configuration to try? I see you have some sysfs tunables. My raid1 array
> consists of two spinning disks and an SSD, all local.
>
> Do you expect this patch to make a difference in my case? With the spinning
> disks marked as write-mostly, I'm getting close to the read performance of
> the SSD (except for very small random reads, for some reason).
>
> It's random writes that are much slower than with only the SSD.
>
> --
> Andras Korn <korn at elan.rulez.org>
> There is no spoon(). But there is a fork().
> --
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--
Roberto Spadim
Spadim Technology / SPAEmpresarial
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