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Re: [Xen-users] RAID-1 strategy for a Xen/CentOS server?

FWIW, "this box" has 4GB RAM atm, expandale to 8GB.

IMHO that means nothing... if it's handling 4 mailboxes, it's overkill, if it's handling 40,000 you're probably dead before you even started... but then you could come up with particular examples where the roles of that 4 and 40,000 could be reversed... e.g. support@xxxxxxxxxxxxx, abuse@xxxxxxxxxxx, etc versus 40,000 never used freebie accounts that are included with some other product...

"If you are using RAID-1 to help to ensure that your system stays up in the
event of a hard disk partition failure, you should consider raiding your
swap partition(s).

No argument. Generally my thinking with respect to raid 1 is to reduce the chance of data loss, but as per the introductory clause, there can be different goals.

My broad-brushstroke goals -- for the whole system,as well as for individual
DomUs -- include:

(1) Maximize failover capability

??? By definition, "failover" requires redundant hardware, sort of the opposite of cutting up a big machine into smaller pieces (xen). If you want failover capability, see linux-ha.org ... and you need to be able to get at the data from the redundant hardware... it's a rather different picture than a normal server setup.

Stuffing DRBD under the vbd's so that a redundant server can mirror the block devices is fine start :) ... but that certainly isn't what I thought you meant by hardware vs software RAID... and you're entering the world of network attached storage....

(2) Minimize potential fordata loss due to HW failure
(3) Maximize the performance of the system

(I've given up on running at less than 10W total power utilization ... ;-) )

You're correct -- in answering my misstated question.  I *meant* to ask:
What's the recommended FS for the Dom0 Xen host?

it is basically irrelevent, as anything that will boot xen is pretty much sufficient. dom0 isn't supposed to do much work (beyond having the kernel relay I/O requests to the real hardware). If you're using file images instead of block devices for your domU vbd's then it may be relevent... but ext3 should be fine. I can't really imagine a scenario where the more esoteric filesystems would be needed... but I'm no expert, and when you get into journalling filesystems (in the domUs) there are some complex interactions (e.g. preserving the order of writes, which is one reason why using real block devices instead of files may be better).

(Then again, using disk files for filesystem images probably conflicts with maximizing failover capabilities... this may depend on how many domUs you have, and whether you need/want to be able to fail them over independently.)


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