On Jun 7, 2012, at 3:09 AM, Daniel Kalchev wrote:

> 
> 
> On 06.06.12 03:16, Scott Long wrote:
> 
> [...]
>> Each disk has its own UFS+J filesystem, except for
>> the SSDs that are mirrored together with gmirror.  The SSDs hold the OS image
>> and cache some of the busiest content.  The other disks hold nothing but the
>> audio and video files for our content streams.
> 
> Could you please explain the rationale of using UFS+J for this large storage. 
> Your published documentation states that you have reasonable redundancy in 
> case of multiple disk failure and I wonder how you handle this with "plain" 
> UFS. Things like avoiding hangs and panics when an disk is going to die.

Redundancy happens by allowing the streaming clients to choose multiple other 
sources for their stream, and buffer enough of the stream to make a switchover 
appear seamless.  That other source might be a peer node on the same network, 
or might be a node that is upstream or on a different network.  The point of 
the caches is to hold as much content as possible, and we've found that it's 
more effective to maximize capacity but allow drives to fail in place than to 
significantly reduce capacity with hardware or software RAID.  When a disk 
starts having problems that affect its ability to deliver data on time, any 
clients affected by it simply switch to a different source.  When the disk does 
finally die, it is removed from the available pool and content is reshuffled on 
the other drives during the next daily content update.  Once enough disks fail 
that the cache is no longer effective, it gets replaced.

Scott

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