[mythtv-users] Minimal hard drive specs for HD recording. (RPM, buffer size, SATA I, II, or III ?)

Steven Adeff adeffs.mythtv at gmail.com
Thu Sep 29 20:15:30 UTC 2011


On Thu, Sep 29, 2011 at 9:51 AM, linux guy <linuxguy123 at gmail.com> wrote:
>
>
> On Thu, Sep 29, 2011 at 4:07 AM, Richard Morton <richard.e.morton at gmail.com>
> wrote:
>>
>> Yes seek time is very important.
>
> Does this warrant 7200RPM drives ?

doesn't hurt

>> I would doubt that one hd could record 2 hd streams while serving 3
>> frontends with hd streams, and this is with commflagging and other processes
>> reduced to the bare minimum.
>
> OK.
>
>> I have one hd recording 4 sd shows and 2hd shows while serving 1 frontend
>> and comm flagging 1 show... this overwelms the drive on occasion.
>>
>> Db and os are on a seperate drive.
>
> So how should I set things up then ?  Should I have 1 hd for each HD-PVR ?
> And if so, what prevents all 3 front ends from accessing content on 1 drive
> ?

database and recordings should never go on the same drive, generally
the database is fine to be on the system (root) drive.

My system:
http://www.mythtv.org/wiki/User:Steveadeff#Current_Dedicated_Back_End

I have six 500GB 7200RPM 8MB cache drives.
I have 3 typically active frontends.
I have a Ceton 4 tuner CableCard tuner, two QAM tuners, and one HDPVR.
I have had instances with all the tuners recording HD, including 2
virtual tuners on the QAM while two frontends were being used for HD
playback. My disk i/o never became an issue.

My findings from my playing with my system come down to one 7200RPM
drive can handle 3 HD read/write streams without getting into trouble.
With my older 5400rpm drives more than two would become an issue.

The HDPVR changes that a little in that in that it has a lower bitrate
due to the h264 compression used vs the standard MPEG2.


>> As you are using hdpvrs I presume all content would be high bitrate
>> recordings.
>
> Yes, if recording HD, which we will be at every opportunity.
>
>> As a minimum I would look at using two drives with large partitions, not
>> in raid and each setup in myth storage groups with spreading of load based
>> on i/o load.
>
> I have no idea how to do that.   Could you point me to some documentation ?

I would suggest, for your setup, at least two drives. Read speeds
occur faster than writes, so since your loads are mostly read loads
from the multiple frontends, this should be fast enough, especially
for HDPVR tuners. Set them up as one large partition per drive for
recordings, and use them in storage groups as opposed to RAID or LVM.

when you set up MythTV for the first time in mythtv-setup there is a
section for storage groups, here you would point your default group to
the two partitions you have set up. read the MythTV wiki for further
help.

-- 
Steve
http://www.mythtv.org/wiki/User:Steveadeff
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