xtreemfs usecase scenario - little help?

[copb.p...@gmail.com]

Mostly looking at viability, for the record.

We have some number X machines running ubuntu on the same LAN. Looking like four machines right now. What is asked of me is to consolidate their storage so that user home folders can be accessed from any machine. I started to just dumb-end three machines and move all hard drives to the fourth, but I'd rather not - these machines are respectable off-the-shelf and may be useful for running Hadoop/etc. So I'd like to keep the hard drives in them.

That being said, the only real requirement that I dont see in documentation is that I can't have a deadlock between machines for boot order. That is, if I boot any given machine, it can't hang on the other three+ machines booting. Can a shared mount in XtreemFS for user home folders fulfill that requirement? If so, how?

Ideal solution: The /home directory is a shared mount, boot isn't deadlocked (machines can be brought online in any order), and the only requirement to guarantee access to a user's home folder is that the physical drive it is on be online. Some degree of replication exists - one drive could go down without losing any files.

Notes? Help? Profanity?

[Robert Schmidtke]

Hi,

for mounting an XtreemFS volume, you need to have the DIR and MRC services running. So during boot of any machine, e.g. when mounting through fstab (http://www.xtreemfs.org/xtfs-guide-1.5.1/index.html#tth_sEc4.3.3), the DIR and MRC must be up already. That is, you need to have one machine that is up first hosting DIR and MRC (and an OSD), then the others can boot (they will each host an OSD). Note that DIR and MRC replication is currently experimental as we're aware of race conditions during failover. We therefore do not recommend using this feature in production. This effectively means that DIR and MRC are single points of failure.

That being said, I'd like to try and understand your situation completely. You have four machines, each with a disk, and they should share a home that is distributed and replicated among them? I would recommend not using /home directly, but /mnt/xtreemfs/home (or similar), to have a local home on each machine in case there are startup problems, so you can still access the machines. You could also make one machine the file system server (add three more disks, start three OSDs on this machine, one on each disk, use replication factory of three). This should also be possible with NFS, which might be better suited for this use case.

I hope I could clarify a bit, please let me know if I missed something or you have additional questions.

Cheers

Robert