[mythtv] Storage Groups - OK to move files between directories in same group ?

[Albert Graham]

Denys Dmytriyenko wrote:
> On Mon, Mar 17, 2008 at 03:19:27PM +0000, Albert Graham wrote:
>   
>> Dave,
>>
>> Well, you're right, I'm also trying to keep the machine as cool as 
>> possible when there is no need for it to be hot, just because drives are 
>> spinning, the drive temps run about 55C which is close to the spec of 
>> 60C, this is because they are packed so close to each other, also, when 
>> I umount and  spin these drives down  (e.g. sdparm -C stop /dev/sdb), 
>> the machine is almost silent, two small fans behind the drive enclosures 
>> (controlled by sensors) spin down to silent mode and the drive temps 
>> drop to about 25C
>> (when spun down).
>>
>> The QX9650 Quad Core runs at 19c when myth backend is recording 
>> (@33Ghz), and 25c (@4Ghz)
>>
>> I do have a separate frontend (laptop sitting on top of my Sky box (UK).
>>
>> You can also see I've got a mega fan which runs about 600rpm (and is 
>> practically silent - speed is controller manually from the front (below 
>> the water tank). This fan is absolutely amazing.
>>     
>
> Quite impressive. I have something similar though, with more, but smaller 
> disks. I set them up to automatically go into standby (spin down) after a 
> period of inactivity (say, 30 minutes) - "hdparm -S 241 /dev/sda". They are 
> still mounted and when something accesses them (recording starts, or frontend
> starts streaming), they are spun up again. The only difference is I don't have 
> RAID on them. If you do hardware RAID (even fake-raid), the whole array is 
> presented as a single /dev/sd? device and you cannot spin it down. Not sure if 
> you can spin down individual /dev/sd? drives under a software /dev/md? RAID...
>
>   
I'm using 3ware 9650SE 12 Port (using 10) and you can spin any array 
down no problem, but it can be a bit slow to spin-up as it staggers the 
spin up so as not to overload the power supply.

Interestingly, there is a nice MythTV Raid doc: 
http://www.mythtv.org/wiki/index.php/RAID#Spinning_down_hard_drives

Unfortunately, this does not work for my controller, or more 
specifically, the hdparm issues the command you mention, but only sdparm 
works on my controller, which means the only way to safely (that I know 
of) spin down, is to umount (flushes buffers/cache) and issue the stop 
command (if there is another way please let me know).

The array is seen as a single drive e.g. /dev/sdb, but smartmon-tools 
can access the disks via /dev/twaX for status/diagnostic tests whihc is 
how I monitor the temps.

> BTW, checked your pictures and noticed you use 5-in-3 enclosures, like ICY 
> DOCK. I also started with them, but then found out they don't provide adequate 
> cooling and drives make vibrating noices from time to time, as rails are all 
> metal. So I replaced them with custom made 5-in-3 brackets with big 120mm fans 
> in front of them. That keeps drives temperature around 40C.
>   
Amazing!, I did have the exact same noise issue, until I decided to fix 
the rattling handles and badly vibrating fans, what I did is to cut a 
very thin strip of rubber-ish  sticky (one side)  material (a bit like a 
plaster - don't know the name of it) and I stuck it parallel to the 
handle on the inside, so when the handle closes, it "locks" into place - 
into the rubber - 100% silent.

The fans that comes with the ICY Dock's are very noisy, I threw them and 
the bracket system away, then replaced them with 3 pin fans connected to 
the motherboard (ASUS QFAN) system with motherboard sensors to control 
the FAN speeds based on the temps of the ICY Docks, I also used rubber 
fan silencers on both sides (internal and external) for each fan.

Because there is very little heat coming from the motherboard as the 
chip sets are also water cooled (Maximus Formular SE), the heat gets 
sucked into the center of the box (i.e. all heat is now ambient), the 
main monster fan then instantly sucks all heat out, you'll also notice 
that there is an empty 5 1/4" bay free between the Icy Docks, the is for 
cool air inflow from the front - this helps cool the Icy Docks and drives.

It also has an 850W dual heat-pipe silent power supply -  
(http://www.endpcnoise.com/cgi-bin/e/std/sku=zm850-hp.html)

So all this takes care of noise from the drives and keeps them very 
cool, The monster fan is controlled manually via the coiled dial at the 
from of the box (as is the FAN on the radiator by the same dial), so I 
can turn this right down so it just hovers and is inaudible for the most 
part.

So the only noise is from the writing to disks from MythTV recording, 
which brings me back to my original question? Storage Groups Semantics!

-

There is one remaining issue that I have and that is the way in which 
MythTV writes files to disk, it seems to be force flushing every  single 
write (about 3MB/s at a time) which is crazy, this causes continuous 
disk activity and I just don't see the reason for it!, I've got 8G ram 
and have set the following in /proc/sys/vm:

dirty_ratio = 90
dirty_background_ratio = 90
dirty_expire_centisecs = 12998
dirty_writeback_centisecs = 0
vfs_cache_pressure = 100
swappiness = 60

But it still flushes every write!, why?

I know this is going to be a tough issue to discuss on this list because 
I'm sure things are done the way they are for very good reason, but 
that's another thread.

Albert.


> Regards,
> Denys
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