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I have an ISCSI SAN that we purchased to store images for our cluster (2TB of images). After reading, we probably should have gone with a NAS rather than a SAN, but back to the point.

I'm going to need two servers to share a single LUN on the SAN for failover. We have haproxy and nginx setup on these two centos 6.5 machines. We're using keepalived to share a virtual ip between these two machines in case one crashes. Similarly, we need the iscsi lun to be available on whichever machine is active so we can serve images to our cluster.

Is there a "simple" way to make this happen?

  • I'm not sure which iSCSI SAN you're using and if it allows you to present disks that are already being presented. However, it's possible to present one disk to multiple clients using TGTd on CentOS. However, it depends if you're using a clustered file system or not as to whether you can mount the disk simultaneously on each client. I've done this with GFS... but as we know, GFS is horribly slow and old. – jaseeey Jan 31 '14 at 4:45
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A clustered filesystem is not a requirement.

The "simplest" way (but not at all simple) is to use HA LVM. See High Availability LVM

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    Looks like a PITA compared to buying a NAS haha. – Brian Lovett Jan 31 '14 at 17:01
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As was mentioned in your other question, you need a clustered filesystem on the shared LUN.

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  • THis is slightly different since only one machine would ever write to the LUN at any given time. I was hoping to get away with a simpler solution for the load balancers because of that. – Brian Lovett Jan 31 '14 at 17:02
  • Then use a NAS. You can't safely share block level access to a LUN using a filesystem that doesn't know it's shared. – mfinni Jan 31 '14 at 17:04

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