On 12/12/2011 09:13 AM, Rudi Ahlers wrote:
On Mon, Dec 12, 2011 at 3:52 PM, Reindl Harald h.reindl@thelounge.net wrote:
Am 12.12.2011 14:49, schrieb lhecking@users.sourceforge.net:
Outage is one thing, but having the disk volumes disappear mid-transaction can be detrimental to a file system's health.
To get this back on-topic and closer to the OP's requests, are there any particular iscsi settings one should consider to increase resiliency and minimise the impact of e.g. a rebooting switch? timeout settings? The big disadvantage of iscsi is that you add another layer that can fail (compared to having virtual machine images on a local disk).
you should always have two links to your iSCSI device and two different switches so that it does not matter if one switch dies or reboots
And then you still have the iSCSI applicance / server to worry about. It can fail as well. Even with redundancy PSU's it could fail - the RAM, CPU, motherboard, controller card, expensive RAID card, etc can fail as well.
I handle this by setting up two servers running DRBD in active/active with a simple two-node red hat cluster managing a floating IP address. The storage network link uses a simple Active/Passive (mode=1) bond with either link go to separate switches.
I've been able to export the SAN to a second cluster, managing the SAN space using clustered LVM, to back VMs. I can live-migrate the VMs between nodes and totally fail the primary SAN and the backup will pick up seemlessly, VMs don't need to reboot.
This offers a substantially less expensive HA option than some commercial HA SAN solutions and avoids the headaches of multipath (which only makes the link redundant, not the SAN itself).