> -----Original Message----- > From: centos-bounces at centos.org > [mailto:centos-bounces at centos.org] On Behalf Of Ross S. W. Walker > Sent: Sunday, March 04, 2007 10:44 AM > To: CentOS mailing list > Subject: RE: [CentOS] CentOS 4.4 lvm and drbd 0.8? > > > -----Original Message----- > > From: centos-bounces at centos.org > > [mailto:centos-bounces at centos.org] On Behalf Of Johnny Hughes > > Sent: Sunday, March 04, 2007 7:16 AM > > To: CentOS ML > > Subject: Re: [CentOS] CentOS 4.4 lvm and drbd 0.8? > > > > On Fri, 2007-03-02 at 15:35 -0600, Les Mikesell wrote: > > > Johnny Hughes wrote: > > > > On Tue, 2007-02-27 at 00:20 -0600, Les Mikesell wrote: > > > >> Johnny Hughes wrote: > > > >>> I am not quite sure that drbd-8 is totally ready yet > > for prime time. > > > >>> Not that I don't trust them (I use drbd in production > > and I love it), > > > >>> but I want to wait for an 8.0.1 or 8.0.2 level before > I move the > > > >>> enterprise CentOS RPMS to that version. > > > >>> > > > >>> I would be open to producing some 8.0.0 rpms for > > testing ... though that > > > >>> will probably need to wait until after CentOS 5 Beta is > > released. > > > >> Could you get the same effect by running software RAID1 > > with one of the > > > >> drives connected via iscsi? > > > > > > > > Provides the same effect as DRBD? ... not really ... as > > DRBD provides a > > > > second machine in hot standby mode with a totally synced > > partition that > > > > is ready to take over on a failure of the first machine. > > If the first > > > > computer blows up (power supply, hard drive crash, etc.), > > the second one > > > > starts up and takes over with no down time (except the > > time it takes to > > > > mount the partition and start the services on the new machine). > > > > > > How is the mirror/sync different than RAID1, and how is > > DRBD's version > > > different than you would have if you exported the 2nd machine's > > > partitions via iscsi and mirrored the live machine using md > > devices with > > > one local, one iscsi member for each? If that is actually > > possible, I'd > > > expect those general purpose components too be much better > > tested and > > > more reliable than little-used code like DRBD. Does DRBD > > have special > > > handling for updating slightly out-of-sync copies or does > > it have to > > > rebuild the whole thing if not taken down cleanly also? > > > > I have no idea how it works, other than it uses the md device > > and raid 1 > > kernel code to mirror the drive/partition to a second machine > > ... and do > > so in real time. It uses heartbeat to create a cluster and > does real > > time failover. > > > > It does not require rebuilding the whole device if shutdown > > uncleanly ... it syncs from the last updated point. > > > > My point was that the 0.8 (actually renamed 8.0.0) code was just > > released. The 0.6 and 0.7 code has been out and stable for quite > > sometime and I have been using it for more than 2 years. > > 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. If you do plan on using MD over iscsi why not try something interesting like a RAID level other than 1, say a RAID 3,4,5,6 and get some increased performance over drbd and regular iscsi. You need a later kernel that supports MD bitmaps to prevent complete re-sync on disconnect and the storage would have to all be local, but say you have a bunch of servers all with direct attached storage and you wish to consolidate storage, but want to leverage all your existing direct-connect. You can have each server export it's storage via iSCSI have a central server that mounts all this storage and creates a fault tolerant MD RAID out of it, creates a LVM VG on top then re-exports it via iSCSI to different platforms. -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.