Markus Hochholdinger wrote:

well, my idea of HA is as follows:

- Two storage servers on individual SANs connected to the Xen hosts. Each storage server provides block devices per iscsi.

- On domU two iscsi block devices are combined to a raid1. On this raid1 we will have the rootfs.

Advantages:

- storage servers can easily upgraded. Because of raid1 you can savely disconnect on storage server and upgrade hard disk space. After resync the raid1 you can do the same with the other storage server.

- If you use a kind of lvm on the storage servers you can easily expand the exportet iscsi block devices (the raid1 and the filesystem has also to be expanded).

The same goes for Hearbeat/DRBD/GNBD I would guess.

- You can make live migration without configuring the destination Xen host specially (e.g. provide block devices in dom0 to export to domU) because all is done in domU.

GNBD clients are more or less stateless.

- If one domU dies or the Xen host you can easily start the domUs on other Xen hosts.

Disadvantages:

- When one storage server dies ALL domU have to rebuild their raid1 when storage this storage server comes back. High traffic on the SANs.

You will also have to rebuild a volume if a XenU dies while writing to disk.

 - Not easy to setup a new domU in this environment (lvm, iscsi, raid1)

iSCSI for rootfs sounds lke a lot of pain.

Not sure:

- Performance? Can we get full network performance in domU? Ideal is we can use full bandwith of the SANs (e.g. 1GBit/s). And if the SANs can handle this (i will make raid0 with three SATA disks in each storage server).

Per.
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