[mythtv-users] Switching backend IDE drives to libata with 2.6.28 kernel

belcampo belcampo at zonnet.nl
Mon Jun 1 19:22:20 UTC 2009

Tom Dexter wrote:
> On Mon, Jun 1, 2009 at 2:23 PM, belcampo <belcampo at zonnet.nl> wrote:
>> Tom Dexter wrote:
>>> I'm in the process of upgrading my various Gentoo machines from 2.6.27
>>> to 2.6.28.  All the current recommendations call for moving from the
>>> old IDE drivers (ATA/ATAPI/MFM/RLL) to the new SATA/PATA drivers
>>> (libata).  I've made the move on one of my non-MythTV boxes and I have
>>> some questions/concerns about the move, especially regarding my
>>> backend machine.
>>> I'd especially like to hear from anyone using the libata with IDE
>>> drives on their backend machines.
>>> A number of hdparm settings aren't supported with libata.  The idea is
>>> to have the kernel just choose the ideal setting.  DMA gets set
>>> automatically and isn't an issue.  32 bit IO (the -c option) isn't
>>> supported, but all current opinion indicates that that setting is not
>>> required these days.  The same goes for the interrupt-unmask (-u).
>>> The one that has be a little concerned is the multiple sector I/O
>>> hdparm setting (-m) which isn't supported either.  From what I've seen
>>> so far, libata seems to default this to 8 when the drives max is 16.
>>> Except for WD drives, I don't see anything in the hdparm man page that
>>> would lead me to believe that 8 would be better than 16.  As a matter
>>> of fact, I never even used the -m option in hdparm, as the old driver
>>> defaulted to 16.
>>> My backend has two 500GB Seagate IDE drives.  I haven't had a good
>>> opportunity to get rid of my lvm partition in favor of storage groups.
>>>  The lvm spans the drive that also has the / partition and the MySQL
>>> databases.  I know that's not an ideal setup, but adding a drive would
>>> be nightmarish, and in any case, it currently works fine the way it
>>> is.  I can record three HD shows at once while watching another
>>> previously recorded program with no problems at all.
>>> I really don't think I can afford to loose even a hint of disk
>>> performance on that setup, which is why I started looking so carefully
>>> at this one.  Any advise would be appreciated.
>> 3 HD-shows at an unrealistic 33Mb/s calculates to 100Mb/s = 12.5MB/s
>> Even an average drive from 2-3 years old does ->50MB/s, this is sequential I
>> know, but never the less.
> I agree that overall transfer rates wouldn't be an issue.  But I'm
> still concerned about the multiple sector I/O setting because of all
> the concurrent stuff going on including recording, playback, and
> database reads/writes.  Even with my current setup, if I'm recording
> three shows and also watching something at the frontend, starting up a
> few commflagging jobs can cause an occasional IOBOUND error.  That
> tells me I don't have much room to loose any performance.
That's probably because of the 'less then optimal' settings for 
buffer-settings in the internal player. Over the years a lot of users 
where suffering from stuttering because of this.
> Tom
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