[mythtv-users] Is there a distributed filesystem available?

Debabrata Banerjee davatar at comcast.net
Tue Jun 20 01:34:41 UTC 2006


I already have several other raid arrays in my myth box for other purposes, 
I am quite sure this is not what I want. If I suppose nothing to meet these 
requirements exist, this could be easily implemented in mythtv, actually it 
'sort of' does it right now if you use multiple backends with storage. It 
just can't manage the storage and can't have more than one per server. In my 
setup I could lose every disk besides one and still have some video data and 
an operational system. It would still record the daily show tonight. Also 
it's some protection against file system corruption (and it actually 
happened to my /myth filesystem, completely trashed)..

RAID is slow, complicated, wasteful, and overkill for myth. A single disk 
can handle many streams of video. A fault-tolerant filesystem and JBOD is 
what I want.

*sigh*

----- Original Message ----- 
From: "Chris Henderson" <jchendo at gmail.com>
To: "Discussion about mythtv" <mythtv-users at mythtv.org>
Sent: Monday, June 19, 2006 8:01 PM
Subject: Re: [mythtv-users] Is there a distributed filesystem available?


> On 6/20/06, Debabrata Banerjee <davatar at comcast.net> wrote:
>>
>> The point would be to _not_ run RAID. I want to run a JBOD with a
>> filesystem
>> that doesn't go belly up with one bad disk, just loses the files that are
>> on
>> that disk. Mythtv recordings can just be re-recorded, the data isn't
>> _that_
>> important. However coming home to a completely broken MythTV blows.. Such
>> things are possible, thought I don't know if possible right now in 
>> _linux_
>>
>>
> Hi All,
>
> Ummm RAID 5, is _exactly_ what you are looking for.
> If RAID 5 is setup correctly you can lose one entire disk and the whole
> system keeps RUNNING.
>
> RAID 5 creates parity data that is stored in two different ways. the first
> way is a little bit on each of the disks in the array. the second is to
> create and online spare.
> THe first way, if a disk in the array dies the other disks hold that 
> parity
> data for that disk. (dending on the raid card/config) The data for that
> drive is still availale due to the parity data. UYes it is slower, as the
> required data is then rebuilt on the fly and give out.
>
> The second way, there is a spare disk sitting there and it is only used 
> when
> one dies. The first way is used more in SME (due to cost) and the Second 
> way
> is usd more in Large Enterprised. (cos they dont care about cost, to a
> point)
>
> THe problems with RAID 5 is that it can not be applied to the boot drive.
> And it takes a minimum of three disk to create the array. But if you take
> backups of mythconverg each day to the array then this is not a problem. 
> You
> can boot of a single drive and put the /Video, / , swap on the array if 
> you
> wanted to. Or there was a post not so long ago that delt with taking a
> "Ghost" of the boot & / drive, so that when he was playing with myth, if 
> he
> broke it he would have a working copy to load, using a dvd. then just copy
> over the DB backup to mythconverg and your away.
>
> I setup this for a freind using 0.18.1 with the following arrangement.
> p4 something or other
> 1gb ram
> 1 80GB HDD (boot, swap and root)
> 4 x 200GB HDD raid 5 for the /video partition. (if you foolow the 
> "standard"
> and place every thing under here)
>
> So in then end when the computer boots it only will see two drives. the 
> Boot
> & / drive and the drive for the /video drive. the /Video drive will be 
> close
> to 800GB (you lose a bit for the parity data. upto one whole drive,
> depending on the setup)
>
> This was using a very good raid card that, acually was not that hard to
> setup. I think he got it from work (large enterprise) so it must have been
> supported under linux.
>
> Anyway the other day (a month or so ago) i went over for a BBQ and the
> myhtbox was in bits. I asked what was going on and he said that one of the
> HDD died and he was replacing it. I watched him do it and all he did was 
> go
> into a BIOS type of thing for the raid card and told it to rebuild parity 
> on
> the new drive.
> We came back about 4 hours later (and a lot of beers) and start watching 
> dvd
> on his system.
>
> I think the best bit of this is that is OS independent. Other than the 
> boot
> drive everything is backed up by the RAID. This is how all the biggest 
> most
> high demand servers run.
>
> Also the cost to do this is pritty cheap, and you dont need to mess with 
> the
>
>
> just my 2c worth.
>
> CH
>


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