[mythtv-users] .23/.24 NFS mounting / Storage Groups

[Brent Bolin]

On Wed, Oct 20, 2010 at 6:44 PM, Raymond Wagner <raymond at wagnerrp.com> wrote:
> On 10/20/2010 19:36, Brian Wood wrote:
>>
>> On Wednesday, October 20, 2010 05:23:41 pm Scott wrote:
>>>
>>> On Oct 20, 2010, at 5:22 PM, Brent Bolin wrote:
>>>>
>>>> My current setup is a back end with raid disk storage and tuners.  I
>>>> also have a back end running in a Xen environment as a guest helping
>>>> with commercial flagging.
>>>>
>>>> I also just upgraded my network to GB today.
>>>>
>>>> Flagging from the mythtv guest helps take the cpu load off the primary
>>>> back end, but still puts a stress on disk I/O.
>>>>
>>>> I've been toying with the idea of creating another storage directory
>>>> for mythtv recordings and that being an NFS mount from the primary
>>>> back end.  One of my main concerns is creating a complected
>>>> configuration.
>>>>
>>>> Is this the only way to spread disk usage between systems(NFS)?
>>>
>>> Are the disks really stressed during commflag? I have a single disk SATA
>>> 7200 RPM drive that records 3 HD streams from a HDHR while doing commflag
>>> at the same time. Disk IO has never been a bottleneck on the system.
>>>
>>> If you do want to spread the work, your best bet for simplicity is more
>>> physical drives in the same system. You can use mdtools or LVM to strip
>>> data across two disks. to spread the work.
>>
>> Linear RAID or RAID 0 will "spread the load" and increase apparent disk
>> performance, but also increase the probability of losing the array's
>> contents due to a disk failure, as those systems provide no redundancy.
>
> RAID0 is actually a detriment to recording performance.  If given
> independent drives, MythTV will default to balancing the load evenly across
> multiple drives.  Each drive will only have to seek between the recordings
> it is directly handling.  When doing RAID0,  every disk will be dealing with
> every recording, seeking back and forth between each, and your total
> throughput diminishes accordingly.
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The raid setup is mdadm(md) raid5 with LVM on top(5x1GB sata).  CPU
load(md) is never more then 2%.  Not really interested in any other
raid configurations.

Same type of raid setup on the Xen box.  I do not want to put tuner
cards in the Xen box.

The setup is 6 HD PCI(e) tuners.  So often in prime time I have 6 HD
recordings running and 4 instances of flagging.

So getting back to my original question about spreading the I/O
between systems.  NFS is the only option correct?.  Unlike the xen
guest that streams from the back end for flagging.  Think I read also
different methods of load balancing.