[mythtv-users] Question re: available SATA ports and linux software RAID

[freedenizen]

On Fri, Apr 8, 2011 at 8:55 AM, John Drescher <drescherjm at gmail.com> wrote:
> On Fri, Apr 8, 2011 at 11:36 AM, Tyler T <tylernt at gmail.com> wrote:
>>> > Just FYI, Linux mdadm software will RAID partitions just as well as disks
>>> > (which I have done myself with success on more than one machine). For
>>> > example, you could make a small OS partition and large recordings partition
>>> > on each of your 2TB drives. Then you can RAID-1 the OS partitions and RAID-6
>>> > the recordings partitions.
>>>
>>> The problem is that you are using the same spindle for your OS (and
>>> presumably your DB) and recordings.  That configuration can cause
>>> performance issues.
>>
>> I agree that with only one spindle this can be an issue. But with 8? ;)

<snip>

> datastore3 database # dd if=bacula.sql of=/dev/null
> 16500494+1 records in
> 16500494+1 records out
> 8448252980 bytes (8.4 GB) copied, 11.3197 s, 746 MB/s
>
> datastore3 database # dd if=/dev/zero of=data.dat bs=8M count=1000
> 1000+0 records in
> 1000+0 records out
> 8388608000 bytes (8.4 GB) copied, 19.6487 s, 427 MB/s
>
> datastore3 database # dd if=/dev/zero of=data.dat bs=8M count=2000
> 2000+0 records in
> 2000+0 records out
> 16777216000 bytes (17 GB) copied, 41.9033 s, 400 MB/s

You are testing sequential reads and writes, which is great for myth
recordings but not a good real world test.  Need to test random I/O
and lots of it.