> -----Original Message----- > From: centos-bounces at centos.org > [mailto:centos-bounces at centos.org] On Behalf Of Les Mikesell > Sent: Sunday, March 04, 2007 12:51 PM > To: CentOS mailing list > Subject: Re: [CentOS] CentOS 4.4 lvm and drbd 0.8? > > Ross S. W. Walker wrote: > > > > If you were running a later kernel version of MD, it is conceivable > > that you could create a mirror with a remote storage drive over > > iscsi. > > > > It would be up to you though to figure out how to fail-over to it > > and to limit the bandwidth MD takes to that remote mirror and > > releasize that it will always be fully synchronous and so > > performance may not be the best over a WAN. > > > > You can also use a pair of vise grip plyers to do the job of an > > adjustable wrench, but it will probably strip the bolt in the > > process. > > Unix has always been about combining tools that each do one > job well. If > we already have a tool (iscsi) that exports remote block > devices well, > following standards that would the actual storage to be on non-linux > devices, and another tool (md raid) that mirrors block > devices, why not > combine them instead of inventing yet another special purpose > tool? I > realize that drbd and nbd were developed before iscsi, but now that > there is a standard cross-platform network block device, why > shouldn't > it be used? MD might need some new options to make it work as > efficiently in this scenario, but that seems like a more > useful place to > add features - that is, there might be other situations where MD > mirroring to an external iscsi partition would be useful, or even > combining many iscsi exports into one raid volume. While yes combining tools is the Unix way, there are also some tools that are better suited for a task than others. For example in my second post I suggest if you have a bunch of direct attached storage, say located on 20 servers in a local area network. If you export the storage from those 20 servers to a central server via iSCSI and use MD raid to create a large RAID-{3,4,5,6} array of those iSCSI targets. Then you use LVM to split those into differing volumes for re-export via iSCSI. You can then use drbd on those LVM volumes with asynchronous replication to a storage array off-site for DR purposes or to a local storage device as a volume snapshot server (where both copies need to be active at once). You can then re-export those volumes via iSCSI to different OS platforms to use as storage. This could work well, but if you plan on using MD RAID1 to replicate data to off-site storage you will see very poor performance. MD RAID1 may work well in replicating storage synchronously between 2 local storage devices, but not to a remote storage device. In that case drbd would work better in that case. Also if you wanted both sides of a mirror to be active at once drbd 8.X is the only way to go. -Ross ______________________________________________________________________ This e-mail, and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail, you are hereby notified that any dissemination, distribution or copying of this e-mail, and any attachments thereto, is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender and permanently delete the original and any copy or printout thereof.