"RAID" for remote filesystems

[Joseph Sinclair]

two questions:
1) How does nbd deal with the differential latency issue?  If latency differs by too much a RAID system will end up with stripes on different "disks" out of order, and things get REALLY messed up at that point.
2) What is RAID 6?

Dan Lund wrote:
> I've done work like this with the network block device as an
> experiment in several different ways.
> To put it in a nutshell I had a machine exporting a couple of nbd
> (network block devices), and I accepted them on another.  They showed
> up as /dev/nbd/0, /dev/nbd/1, etc.
> I then made a raidtab that took them and set them into a RAID5 and had
> a hotspare.
> I've tested it with RAID1/5/5+1/6/6+1, made it failover, hot-added
> "drives", etc.
> 
> It was pretty decent in throughput, and I was about ready to put
> together a turnkey solution for my work as an expandable disk
> subsystem. (on it's own gig backplane)  I made sure it was on it's own
> gig backplane because the nbd devices are solely dependant on the
> network.  If it so much as blips, your disks go away.
> RAID, as far as I know, only works on block devices.
> You could always check out PVFS, or Coda if your looking for something
> on the filesystem layer.  I have far more faith in nbd though.......
> 
> --Dan
> 
> 
> On 10/9/05, Matt Alexander <lowbassman at gmail.com> wrote:
> 
>>I'm wondering if anyone knows if this is possible...
>>
>> Take multiple remote filesystems such as NFS, gmailfs, Samba, sshfs, and
>>layer a filesystem over the top to create one namespace.  Ideally it would
>>provide some fault tolerance/redundancy and improved performance by using
>>the concept of RAID over the multiple connections.
>>
>> In reality, this new filesystem layer wouldn't care if the filesystems are
>>remote or not.  You could have...
>>
>> /mynfsmount
>> /mygmailfsmount
>> /myothergmailfsmount
>> /mysshfsmount
>>
>> ...and then a new mount point of...
>>
>> /myreallycoolmount
>>
>> ...and when you put files here, they're striped/mirrored over all the
>>previous mounts.
>>
>> Is this currently possible?  If not, then perhaps I'll see if I can make it
>>happen in my minuscule free time.  I know there are a ton of potential
>>problems with this, but it'd be a fun project nonetheless.
>> Thanks,
>> ~M
>>
>>
>>
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> 
> 
> 
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