On Fri, Sep 26, 2008 at 11:39 AM, Chris Picton <chris AT ecntelecoms DOT com> 
wrote:
> On Fri, 2008-09-26 at 10:35 -0400, John Drescher wrote:
>
>> Here is what I get on a 5 drive software raid5
>>
>>  # dd if=/dev/zero of=/bigfile bs=1M count=8192
>> 8192+0 records in
>> 8192+0 records out
>> 8589934592 bytes (8.6 GB) copied, 44.8402 s, 192 MB/s
>
> I have tried testing directly to the block device, to bypass any
> filesystem related issues:
>
> # cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4] [raid0] [raid1]
> md0 : active raid5 sdg1[5] sdf1[4] sde1[3] sdd1[2] sdc1[1] sdb1[0]
>      48877120 blocks level 5, 64k chunk, algorithm 2 [6/6] [UUUUUU]
>
> # dd  if=/dev/zero of=/dev/md0 bs=64k count=65536
> 65536+0 records in
> 65536+0 records out
> 4294967296 bytes (4.3 GB) copied, 57.2713 seconds, 75.0 MB/s
>
> # dd  if=/dev/zero of=/dev/md0 bs=1M count=4096
> 4096+0 records in
> 4096+0 records out
> 4294967296 bytes (4.3 GB) copied, 113.358 seconds, 37.9 MB/s
>
> # cat /sys/block/md0/md/stripe_cache_size
> 1024
>
>
If you can not get enough speed with this. I would recommend single
drives. And looking into some of the disk-changer script threads. This
way you can make your drives look like a 6 drive autochanger. The only
problem I see with this is if you have any jobs that are bigger than 1
TB, bacula generally does not want to switch drives during a backup.

John

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