The RAID subsystem takes care of all of the backend issues like latency to disk and so forth. nbd is merely a block device, and from my experience if a disk even has a single timeout, the disk will be written as faulty by the subsystem and be set to [_]. raid6 is: http://www.synetic.net/Tech-Support/Education/RAID6.htm Essentially it's data and parity striped across the array, and that itself has a parity. You can lose multiple disks with a raid6 setup and not lose data, I use it and I absolutely love it. (mine is raid6+1) On 10/10/05, Joseph Sinclair wrote: > 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 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 > >> > >> > >> > >>--------------------------------------------------- > >>PLUG-discuss mailing list - > >>PLUG-discuss@lists.plug.phoenix.az.us > >>To subscribe, unsubscribe, or to change you mail settings: > >>http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss > >> > >> > > > > > > > > -- > > To exercise power costs effort and demands courage. That is why so > > many fail to assert rights to which they are perfectly entitled - > > because a right is a kind of power but they are too lazy or too > > cowardly to exercise it. The virtues which cloak these faults are > > called patience and forbearance. > > Friedrich Nietzsche > > --------------------------------------------------- > > PLUG-discuss mailing list - PLUG-discuss@lists.plug.phoenix.az.us > > To subscribe, unsubscribe, or to change you mail settings: > > http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss > > > --------------------------------------------------- > PLUG-discuss mailing list - PLUG-discuss@lists.plug.phoenix.az.us > To subscribe, unsubscribe, or to change you mail settings: > http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss > -- To exercise power costs effort and demands courage. That is why so many fail to assert rights to which they are perfectly entitled - because a right is a kind of power but they are too lazy or too cowardly to exercise it. The virtues which cloak these faults are called patience and forbearance. Friedrich Nietzsche --------------------------------------------------- PLUG-discuss mailing list - PLUG-discuss@lists.plug.phoenix.az.us To subscribe, unsubscribe, or to change you mail settings: http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss