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

[Brian Wood]

On Jun 19, 2006, at 10:45 PM, Steve Hodge wrote:

> On 6/20/06, Chris Henderson <jchendo at gmail.com> wrote:
>> On 6/20/06, Debabrata Banerjee <davatar at comcast.net> wrote:
>>> I already have several other raid arrays in my myth box for other
>> purposes,
>>> I am quite sure this is not what I want.
>>
>> OK,
>>
>> But i dont understand. Please exlpain. You say you want a fault  
>> tolerant
>> files system, doesnt Raid 5 give you that?
>
> RAID 5 gives you a high level of fault tolerance at the cost of
> complexity and capacity. What Debabrata wants is a partially tolerant
> setup, basically a file system that can span X disks, and when a disk
> fails it only loses the files on the failed disk (i.e. 1/X of the data
> if it were full). It's sort of in between RAID 0 and RAID 5: RAID 5
> can have a single disk fail without any data loss, RAID 0 will lose
> all data when a single disk fails, this hypothetical filesystem would
> lose some but not all of the data if a disk fails.

Wouldn't simple aggregation (sometimes known as "linear RAID)  
accomplish this? While it would take some specialized measures to  
recover the data on the remaining operational disks the data is not  
"interleaved" the way RAID0 data is (which makes it impossible to  
recover any files larger than a single block if it is partially on a  
failed disk). Also, some files would be non-contiguous, but if you  
used the filesystem just for writing and reading large video  
information files, and perhaps de-fragged often, you could probably  
recover a lot of the information if a single disk failed.

As has happened often in PC history, our storage systems have  
outstripped our backup systems. There is no fast easy way to backup  
today's hard drives without spending an amount equal to the initial  
storage investment. Tape systems with sufficient capacity cost more  
than additional hard drive space, and the most practical alternative  
today is simply some form of redundant hard drive storage.

In fact, for systems under 1tb,  software RAID1 systems are probably  
cheaper than hardware RAID5.