[mythtv-users] Dedicated backend

Simon Hobson linux at thehobsons.co.uk
Mon Oct 1 09:30:46 UTC 2012


>Josu Lazkano wrote:
>>Hello list, I am running MythTV for 3 years on two different
>>frontend/backend ION systems. They work great, but I want to try to
>>add a dedicated backend and use it from differents frontends.
>>
>>I buy a "HP ProLiant MicroServer AMD Turion II N40L":
>>http://h10010.www1.hp.com/wwpc/us/en/sm/WF25a/15351-15351-4237916-4237918-4237917-4248009.html?dnr=1
>>
>>I will add to it 4 tuners:
>>
>>PCIe DVB-S2 Tevii S470
>>USB DVB-S2 Tevii S660
>>USB dual Hauppauge DVB-T
>>
>>It comes with 2GB of memory and a 250GB disk. I will add an other 2TB
>>SATA and 2x1TB SATA (RAID 1).
>>
>>My idea is to use the 250GB disk as system (EXT4), the 2GB disk for
>>recordings (XFS) and both 1TB disk as personal data on a RAID 1
>>(EXT4).
>>
>>My favourite distro is Debian, so I plan to install Debian Wheezy 
>>64bits on it.
>>
>>My questions:
>>
>>1. Is a good option to install 64bits? I always use 32bits.

I use 64bit on anything that supports it.

>>3. Any other advice?

IMO the Microserver is a good choice of backend hardware. Small, low 
power, quiet, and good value.
However, it is lacking in horsepower if you want to do things like 
transcoding - I find mine (the earlier N36L model) can only transcode 
from UK Freeview "to iPad" at about 1/6 to 1/5 of realtime (ie one 
hour of TV takes 5-6 hours to transcode). This isn't a problem if you 
think ahead, but it is if you want to do realtime transcode (eg for 
HLS? streaming) or want to take a "just aired" program with you to 
watch while travelling.

I'd be tempted to mirror a couple of small partitions on the 1TB 
drives for the system drive etc. With your plan, you will have 
redundancy for your personal data, but not the system.
I used md to make mirrored arrays* for /boot and /, and a larger one 
for an LVM PV which I can then divide up as required (I currently 
only have /var and some spare space in it). Install grub on both 
drives, and the system can boot from either - and if a disk fails, md 
will take care of keeping you running from the other until you 
replace the failed one.

* You only need the boot partition to be mirrored so grub can read 
either one. After that, the root partition can be whatever your 
initrd and kernel have support for.


Pieter De Wit wrote:


>3) Have you thought of putting the 2x1TB and 1x2TB into a LVM array 
>and stripping the data (you can mirror *insdie* LVM, but it needs 3 
>drivers to be statefull - as in commited to disk, otherwise it 
>re-syncs after a reboot) - perhaps an idea :)

Bad idea for this application.
Myth will handle multiple filesystems for recording storage - and it 
will automatically spread load between them. If you stripe several 
disks together then you can potentially significantly reduce 
performance.
You also reduce reliability - if one disk fails, you lose the lot. 
Eg, if you stripe 3 identical disks together you decrease MTBF by 3 
and increase the amount of data lost by a disk failure by 3 - 
depending on how you measure it, your risk has gone up between 3fold 
and 9fold.

And in the OPs case, he is using different disks, in different 
configurations, for different purposes.

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.


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