[Cluster-devel] GFS + iscsi target + LVM performance and file integrity

[Christine Caulfield <ccaulfie@redhat.com>]

???? Anuj Singh wrote:
> Hi,
> I have a question related to GFS + LVM and iscsi.
> 1). I have a file test.txt on shared GFS file system, some user ramesh
> opens test.txt to read, at the same time some other user Smith on the
> network writes some data to test.txt file.
> What data will Ramesh see in test.txt file which is changed after he
> opened?
> How does GFS handles data integrity?

The same thing happens on GFS as would occur if you did that on a local
file system. GFS does not provide any additional data integrity features
over other file systems. If you can corrupt a file by writing to it from
two places using ext3 on one node, then the same thing will happen using
GFS, regardless of whether the processes are on the same or different nodes.

The point of GFS is not to provide data integrity, but /metadata/
integerity. ie, the filesystem itself does not become corrupted by two
nodes writing to the same inode or directory.

So, the basic rule is: if it would corrupt data if two people on the
same node did it on next3, then it will also corrupt data if two people
on different nodes did it on GFS.

I hope that's clear!
-- 

Chrissie