Thank you for the clarification. I have one more question.
I've seen some web page by redhat and it says that gfs2 has a poor filesystem performance (i.e. throughput) compared to xfs or ext4. [image: image.png] In a high performance hardware environment (nvme over fabric, infiniband (56G)), I ran a FIO benchmark, expecting GFS2 to be comparable to local filesystems (ext4, xfs). Unexpectedly, however, GFS2 showed 25% lower IOPS or throughput than ext4, as the web page results. Does GFS2 perform worse than EXT4 or XFS even on high-performance network + storage? Thank you, Daegyu ᐧ 2019년 8월 9일 (금) 오후 8:26, Andrew Price <anpr...@redhat.com>님이 작성: > On 09/08/2019 12:01, Daegyu Han wrote: > > Thank you for your reply. > > > > If what I understand is correct, > > In a gfs2 file system shared by clients A and B, if A creates /foo/a.txt, > > does B re-read the filesystem metadata area on storage to keep the data > > consistent? > > Yes, that's correct, although 'clients' is inaccurate as there is no > 'server'. Through the locking mechanism, B would know to re-read block > allocation states and the contents of the /foo directory, so a path > lookup on B would then find a.txt. > > > After all, what makes gfs2 different from local filesystems like ext4, > > because of lock_dlm? > > Exactly. > > > In general, if we mount an ext4 file system on two different clients and > > update the file system on each client, we know that the file system state > > is not reflected in each other. > > Yes. > > Cheers, > Andy > > > Thank you, > > Daegyu > > ᐧ > > > > 2019년 8월 9일 (금) 오후 7:50, Andrew Price <anpr...@redhat.com>님이 작성: > > > >> Hi Daegyu, > >> > >> On 09/08/2019 09:10, 한대규 wrote: > >>> Hi, I'm Daegyu from Sungkyunkwan University. > >>> > >>> I'm curious how GFS2's filesystem metadata is shared between nodes. > >> > >> The key thing to know about gfs2 is that it is a shared storage > >> filesystem where each node mounts the same storage device. It is > >> different from a distributed filesystem where each node has storage > >> devices that only it accesses. > >> > >>> In detail, I wonder how the metadata in the memory of the node mounting > >> GFS2 > >>> looks the consistent filesystem to other nodes. > >> > >> gfs2 uses dlm for locking of filesystem metadata among the nodes. The > >> transfer of locks between nodes allows gfs2 to decide when its in-memory > >> caches are invalid and require re-reading from the storage. > >> > >>> In addition, what role does corosync play in gfs2? > >> > >> gfs2 doesn't communicate with corosync directly but it operates on top > >> of a high-availability cluster. corosync provides synchronization and > >> coherency for the cluster. If a node stops responding, corosync will > >> notice and trigger actions (fencing) to make sure that node is put back > >> into a safe and consistent state. This is important in gfs2 to prevent > >> "misbehaving" nodes from corrupting the filesystem. > >> > >> Hope this helps. > >> > >> Cheers, > >> Andy > >> > >> > >> > > >
