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I need a cluster filesystem for an iSCSI device. The problem is that the servers to which it is connected generate datafiles which must be read by every other servers. Except for the writing and deleting of such files, I do not need a full locking scheme like in OCFS2 or GFS2.

So, can I use a distributed lock manager (DLM) on top of an ext3 filesystem or must I use only specialized filesystem ?

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This is a strange question. DLM is part of GFS2. Also GFS2 is not a locking scheme, it's a cluster filesystem that uses a locking scheme to share data. And you want to share data. – niXar Apr 16 '10 at 9:53
Well, I know, but for example OCFS2 use a somewhat restrictive model of distributed lock : no lock, protected read (only one host can read at a time) and exclusive (only one host can access the file). What I need is the ability to read a file, even if it is accessed by another host. – edomaur Apr 16 '10 at 10:13
I don't know how OCFS2 works, but GFS certainly allows concurrent access to the same file. The lock is not per file, it's per FS block. Also the locking is not supposed to be seen by the layers above the filesystem, it's used to handle consistency. – niXar Apr 16 '10 at 10:16
I will try GFS. Just had to ask that question to be sure that it was (or not) a solution. – edomaur Apr 16 '10 at 10:31

2 Answers 2

up vote 7 down vote accepted

NO. The main reason is that the filesystem cache is not cluster aware and is not coherent, so you end up mangling your data.

Try mounting the ext3 FS in two boxes, create a file in one box and see if it appears in the other...

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ok, thanks for the answer. – edomaur Apr 16 '10 at 9:59

A filesystem must be cluster aware, meaning that it has to know to look for the lock manager (or the nodes need to know to look at the quorum disk). You can't just strap on an DLM and have it work. That would be neat, though. Sorry!

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Happy 10k-day Matt ;) – Chopper3 May 12 '10 at 9:30
Thanks chopper! I'm not entirely sure what happened, but horray! – Matt Simmons May 12 '10 at 13:32

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