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Distributed Data Storage on a LAN?
AgentSmith2 asks: "I have 8 computers at my house on a LAN. I make backups of important files, but not very often. If I could create a virtual RAID by storing data on multiple disks on my network I could protect myself from the most common form on data failure - a disk crash. I am looking for a solution that will let me mount the distributed storage as a shared drive on my Windows and Linux computers. Then when data is written, it is redundantly stored on all the machines that I have designated as my virtual RAID. And if I loose one of the disks that comprise the raid, the image would automatically reconstruct itself when I add a replacement system to the virtual RAID. Basically, I'm looking to emulate the features of hi-end RAIDS, but with multiple PCs instead of multiple disks within a single RAID subsystem. Is there any existing technologies that will let me do this?"
Using a pair of Intel EEPro 100's w/ trunking (using both links at the same time on one IP, works w/ a cisco switch), I've gotten over 100 Mb/sec of actual throughput (I think I hit 137 Mbit/sec, peak) out of a box using NBD to create a mirror'd RAID volume over the trunked ports. Now, my actual 'real' data speeds to the file ssystem were about half that (Call it 50-65 Mbit, or 6 to 7.5 MByte/sec), due to mirroring == writing it twice. Still not bad. Yes, the target disks were themselves part of other RAID volumes, for speed :)
In my experience, it's one of those "it would be a wonderful thing if it worked."
It requires it's own partition for each mount of it; you can't just share disks you've already got.
Setup also takes hours, and it probably won't work the first time. Online documentation is incredibly outdated, which doesn't help matters at all. It also takes a hefty chunk of computer to run it, because it requires a lot of watchdog type programs to fix the frequent corruption that happens to it as you use it.
The servers time has to be matched exactly, so it's also best if you've got an NTP server running and clients on all the machines.
It's also about ten times slower than Samba (which you might use instead to share with Windows machines), and it chokes when you try to move/copy/delete large files.
I tried it for a month before it completely corrupted it's own partition and I switched back to NFS and Samba.
I can't wait for the day when these problems are but a memory and such a system works flawlessly.
Mod me down and I will become more powerful than you can possibly imagine!
But say I do? I mean, versioning databases are the next bit, man. Why not have a chmod +v for versioning? If this bit is set, then apply version control. Every file open/write/close sequence adds a new version delta. Sure, there's a performance hit associated with it, but I'd like the choice.
AFAIK, there's at least on project out there to turn CVS into a filesystem, and a few others to add MVCC functionality into a filesystem (somewhat like the Clearcase filesystem does).
It's a good feature, something I'd want on my docs and code, and other specs, not necessarily on my pr0n and MP3s.
-Chris