[Linux-cluster] GFS locks granularity (DLM or GULM)

[Alban Crequy]

Hello,

What is the locking granularity in GFS? Can GFS do range locks? Is the 
granularity of DLM different than the GULM one?

The only explanation I found are:

    «Locking in GFS is closely tied to physical storage. Earlier versions of 
GFS [21] required locking to be implemented at the disk device via 
extensions to the SCSI protocol. Newer versions allow the use of an external 
distributed lock manager, but still lock individual disk blocks of 4kB or 
8kB size. Therefore, accessing large files in GFS entails significantly more 
locking overhead than the byte-range locks used in GPFS.»
    http://www.broadcastpapers.com/asset/IBMGPFS07.htm

But maybe this is outdated?

Other doc:

    «GFS has a couple pf locks for each file. (one for data, one for meta
data, one for iopen counts. maybe others, don't recall off the top of my
head.)  Directories get a lock, as well as most of the interal
structures.  So more-or-less gfs locks at the file level.  (note that
this is not the same or similar to fcntl locking, nor is it compatible.)»
    http://www.redhat.com/archives/linux-cluster/2005-June/msg00016.html

-- 
Alban