[mythtv-users] Wiki: Balanced Disk I/O

[Tom Hayward]

On Aug 11, 2015 8:50 AM, "Peter Bennett (cats22)" <cats22 at comcast.net>
wrote:
>
> Hi MythTV experts
>
> I am updating the wiki and wondering about the Balanced Disk I/O setting.
>
> https://www.mythtv.org/wiki/Storage_Groups#Balanced_Disk_I.2FO
>
> The above page recommends if you are doing more than 2 recordings at once
to use this setting to get recordings put on separate file systems to avoid
buffer overruns. I am thinking of changing that recommendation.
>
> A quick back of the envelope calculation tells me that I could record
some 50 HD programs at the same time on one disk drive, based on 1 Gb/sec
transfer rate and 8 GB per hour on each HD recording.

Your calculation fails to account for seek times between multiple HD
streams, commercial flagging, and playback. You might be able to afford SSD
for recording drives, but I'm not there yet.

My disks write a single stream at max 80-120 MB/s. This goes down
significantly when seeking for commercial flagging or recording multiple
programs. MythTV likes to write data every second and if the disk is busy I
see glitches from dropped data.

Before changing the recommendation, please collect test results for
multiple platforms. Maybe the recommendation for your hardware will be
different than mine. My system benefits from balanced I/O; I've tested both
ways.

Tom
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