On Thu, 2005-06-23 at 08:43 -0500, Troy Dawson wrote: > This idea of fencing is what's throwing me off. If I'm reading things > right, I can't do group GFS without them being in a cluster, and they > can't be in a cluster without doing fencing. But the fencing seems to > just allow the various machines to take over for one another. Actually - fencing prevents hung rogue nodes from being able to corrupt the file system. Believe it or not, power-cycle fencing actually can help more than you think: A node without power can't flush buffers, so after the node is fenced, you can have it turned back on. If it was a software failure, your cluster will resume all normal operations without any manual intervention. > I also don't have access to the SAN switch, other than my machines plug > into it. It's essentially a black box. These machines also don't have > any way to remotely turn power on an off. :( > Is GFS what I really want? I've tried just standard ext3, but I was > getting a caching problem with my read only machines. Do I just want to > try and fix my caching problem? You'll probably need to do synchronous I/O on all nodes. This will likely be slow, but I think your limiting factor will be network bandwidth, not disk I/O times. Note that GFS was designed to prevent "hot spots": places on the disk which are accessed over and over -- like an inode table on ext3, for example. Overuse of hot-spots can cause premature failure of drives. Just things to consider. You can probably do it without GFS, but I wouldn't recommend it. Remote power control does not have to be expensive. E.g.: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=86723&item=5783773234&rd=1&ssPageName=WDVW That's cheaper than replacing ONE enterprise-grade SCSI or FC disk. (Disclaimer: I have no affiliation whatsoever with the seller.) -- Lon -- Linux-cluster@xxxxxxxxxx http://www.redhat.com/mailman/listinfo/linux-cluster
