-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Ross S. W. Walker Sent: Sunday, March 04, 2007 11:00 AM To: CentOS mailing list Subject: RE: [CentOS] CentOS 4.4 lvm and drbd 0.8?
-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@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@centos.org [mailto:centos-bounces@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
When I said local I meant on the local area network.
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
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