[mythtv-users] Fastest RAID for HD?
Roger Heflin
rogerheflin at gmail.com
Thu Feb 14 18:53:39 UTC 2008
John Drescher wrote:
> On Thu, Feb 14, 2008 at 10:36 AM, Ronald Frazier <ron at ronfrazier.net> wrote:
>>> I think the big problem is without tuning MythTV and ext3 want to
>> > write to the array in too small of chunks too frequenty causing
>> > thrashing. As I said before raid5/raid6 are bad when they thrash.
>>
>> What about XFS or JFS?
>> Also, can the OS's write caching be tuned to avoid/minimize the
>> problem (if it even is a problem for the intended usage)?
>>
> I mentioned ext3 because it has a stricter default write policy
> causing it to want to write the data to disk faster.
>
> John
The way to solve this problem is to adjust the code to actually
not write to disk in small chunks (if it is not already) I did some
work before (non-myth) where I was reading 10 streams from slow
network devices at the same time and this caused bad fragmentation,
changing the code with setvbuf to write out 1MByte at a time
make the underlying filesystem behave a lot better, with the
fragmentation trying to read out one of the streams resulted
in very slow reads (1/10 of expected speed), after changing the
buffer size the fragmentation was still there, but in 1MB chunks
rather than 32k/64k chunks which result in alot less thrashing, and
alot better read speeds.
Roger
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