On Mon, Apr 20, 2009 at 12:56 PM, ESGLinux <[email protected]> wrote:
> Hello, > > > > 2009/4/20 Gordan Bobic <[email protected]> > >> On Mon, 20 Apr 2009 18:18:22 +0200, ESGLinux <[email protected]> wrote: >> > Hello, >> > >> > first, thanks for your answer, >> > >> > I suspected it but why can i do it with NFS. ? >> >> Not sure I understand your question. NFS is a network file system like >> CIFS >> specifically designed to be mounted from multiple clients simultaneously. >> ext3 is only designed with a single accessor in mind. > > > I´ll try to explain myself > > I have a partition /dev/sda > > /dev/sda on /iscsivol type ext3 (rw) > > but this partition is a target iscsi on another server. I format the > partition with ext3 but its not a local disk, is a target iscsi. > > with this configuration I have the filesystem corrupted. > > second scenario > > I have > 192.168.1.198:/nfsexport/ 6983168 2839168 > 3783552 43% /mnt > > but the parttion 192.168.1.198:/nfsexport/ is again ext3 the diference is > that I use nfs as network protocol instead of iscsi. > (overly simplified explanation) This is because with iSCSI you are mounting the filesystem directly as a block device. Through NFS, the filesystem isn't accessed directly. The NFS server handles all the actual I/O, so only one system is actually touching the filesystem. > >> > the nodes never are going to be active at the same time so I can mount >> the >> > shares via NFS. With NFS when I create a file in a share automatically i >> > got it in the shared mounted by all the clients. >> >> I still don't understand your question - that is what NFS is designed for. > > > Yes I agree with you, but I thought with iscsi i can do the same as with > NFS. > No, iSCSI and NFS are completely different. One is SCSI encapsulated in Ethernet- the volumes are going to look local to the system. The other is a conventional file sharing protocol. > >> > In this case I don´t need to write to the share concurrently >> > >> > can be this configuration a problem? >> >> No, it's fundamentally impossible. In order to have a FS that can be >> mounted simultaneously from multiple nodes, it has to be aware of multiple >> nodes accessing it, which means that it needs coherent caching. Local file >> systems like ext3 don't have this. When one node writes to the ext3 file >> system, the other node will have cached the inodes as they were >> originally, >> and it won't bother hitting the disk to re-read the contents, it'll just >> return what it already has cached. And almost certainly corrupt the file >> system in the process. >> >> You cannot have a shared ext3 volume with writing enabled. Period. > > > ok understand it, > > but (always there is a but ...) > > I only want to share a directory in which one node writes at one and when > it fails the other node has the diretory mounted with the data and can write > to it. > > Before I have known about cluster my decission would been to mount the > shares with NFS. Now I want to be more sofisticated and want to use cluster > tools, so I thought to mount it with iSCSI instead of NFS, but always with > the ext3 as the underlying filesystem. > > Perphaps this is my mistake. > > any suggestion that makes me see the light ;.) > If you want to have multiple systems access the same volume via iSCSI, you need to use a filesystem that is multiple-node aware such as GFS.
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