[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-users] Network Block Devices & Redundancy
I'm currently looking to establish a small pool of xen hosts, each running several guests, backed by disk servers for the guests, accessible across the network. I'm hoping to achieve ease of migration, and reliability of service (particularly in cases of hardware failure), but I'm not pushing for 24/7 guaranteed HA. I've looked at the different ways of offering network storage to the guests, and have narrowed it down to what I think are the 2 best options: 1) DRBD & Heartbeat (or similar cluster management tool): Run 2 disk servers with one 'master', mirroring in the background. In case of failure of the master, switch the slave to being the master. Advantages: Server-server communication is efficient Recovery only has to update a small delta Disadvantages: Risk of split-brain, if the disk servers stop 'seeing' each other and both try to become masters. 2) Software RAID(1) of iSCSI disks: Export an iSCSI disk from each of 2 disk servers - RAID these together on the host, using multipath and RAID1 to deal with disk failure. Advantages: RAID array degrades 'nicely' - no need to switch master/slave roles etc. No risk of split brain. No human decision making involved during recovery stages Disadvantages: RAID rebuild happens on the host, not between servers RAID recovery requires complete rebuild, not just delta of changes Looking at the above, I am drawn towards the RAID1 option. While it might be less efficient in terms of speed and rebuild times, it completely avoids the risk of split brain, and also there seem to be far fewer places where manual intervention (i.e human decisions where a script can't do the work) might be needed than with DRBD. However, I'm also aware I might be missing something fundamental here. Anyone care to agree with, or enlighten me? Thanks, Matthew -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. Attachment:
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