On Sat, May 17, 2014 at 1:00 PM, Steve Thompson <smt at vgersoft.com> wrote: > On Sat, 17 May 2014, SilverTip257 wrote: > > > Sounds like you might be reinventing the wheel. > > I think not; see below. > > DRBD [0] does what it sounds like you're trying to accomplish [1]. > > Especially since you have two nodes A+B or C+D that are RAIDed over > iSCSI. > > It's rather painless to set up two-nodes with DRBD. > > I am familiar with DRBD, having used it for a number of years. However, I > don't think this does what I am describing. With a conventional two-node > DRBD setup, the drbd block device appears on both storage nodes, one of > which is primary. In this case, writes to the block device are done from > the client to the primary, and the storage I/O is done locally on the > primary and is forwarded across the network by the primary to the > secondary. > What I am describing in my experiment is a setup in which the block device > (/dev/mdXXX) appears on neither of the storage nodes, but on a third node. > Writes to the block device are done from the client to the third node and > are forwarded over the network to both storage servers. The whole setup > can be done with only packages from the base repo. > Right, DRBD is no longer available from the CentOS Extras repo (like it was in EL5). > > I don't see how this can be accomplished with DRBD, unless the DRBD > two-node setup then iscsi-exports the block device to the third node. With > provision for failover, this is surely a great deal more complex than the > setup that I have described. > > If DRBD had the ability for the drbd block device to appear on a third > node (one that *does not have any storage*), then it would perhaps be > different. > Ah, good point. -- ---~~.~~--- Mike // SilverTip257 //