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



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But maybe this is outdated?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


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