On 11/14/10 5:48 PM, Nathan Eisenberg wrote: > > No - no RAID - same disk approach as if you were running 24 nodes - > except the node is configured to use /mnt/disk1, /mnt/disk2, > /mnt/disk3, etc, instead of having a node process for /mnt/disk1, > /mnt/disk2, /mnt/disk3, etc. > > In this way, a 24 disk server only shows up to the gateway as a single > tahoe node, which is desirable.
But you want to see more than one share per machine, right? One machine, one tahoe node, but up to 24 shares land there, yeah? Hmm. We'd have to change a couple of remote APIs to make that work: currently the client uses the nodeid of each server (i.e. the hash of their Foolscap SSL cert) to figure out which shares to send to them. The assumption of one-cert-per-server is wired in a bit deeper than it really ought to be, but it made a lot of the code easier to write and make secure. Some of that hardwiredness may get cleaned up in the signed-announcement-dicts work I'm doing, since I'm trying to lay the groundwork for a move away from Foolscap and towards signed HTTP requests instead. If that works, it should get rid of the 'write enabler' shared secret, and thus remove the need for a confidential channel between client and server, which is a big part of why we index storage servers by their cryptographic id. The easiest way to do multiple-servers-per-process would be to run multiple Tubs per process (one per server). The win, I suppose, would be reduced memory usage (sharing the Python interpreter and Tahoe code between all the servers). The loss would be reduced parallelism: that one process would be doing blocking disk IO one share at a time, whereas running 24 separate processes would give the kernel scheduler more IO parallelism to work with, as well as being able to take advantage of multiple cores. Tahoe is intentionally single-threaded. I'd definitely recommend benchmarking the two approaches for comparison. I'd be worried that single-tahoe-node-for-multiple-disks would be a lot slower, under load, than running 24 separate tahoe nodes, one per disk. cheers, -Brian _______________________________________________ tahoe-dev mailing list [email protected] http://tahoe-lafs.org/cgi-bin/mailman/listinfo/tahoe-dev
