Ruediger Meier wrote:
On Wednesday 05 June 2013, Dave Howorth wrote:
Ruediger Meier wrote:
I'd benchmarked it and it's not faster for me. The advantage is that in case of inconsistencies you will get always the same data from one particular mirror. I'd say that's a fairly unusual and worrying case.
Generally using both could be even slower if you have one fast and one slow HD.
Whilst true, I'd say that was also unusual and something to be avoided.
BTW it's a valid use case to safely place one of the mirrors far away connected via network or SAN. That's why you can set write-mostly and write-behind, see man md:
"This allows for a RAID1 with WRITE-BEHIND to be used to mirror data over a slow link to a remote computer (providing the link isn't too slow). The extra latency of the remote link will not slow down normal operations, but the remote system will still have a reasonably up-to-date copy of all data."
cu, Rudi
Thanks very much for that explanation, Rudi. I've used md raid for years and never knew that. Come to it, I've never read the md man page before and that is a very useful summary of the concepts! It sounds a useful capability to have a remote mirror using those facilities. What I'm not clear about yet is how that fits in with the stuff on top (i.e. LVM and the filesystems). I'm supposing that the RAID has no idea about consistency of filesystem metadata for example, so whilst the data on the mirror might be fairly recent, I don't see how there can be any expectation that it is consistent? But I expect I need to do some more reading. Cheers, Dave -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org