I have an IBM xSeries with 6x SAS 74.8GB 10K discs which I will use as a virtual host (either VKM, Xen or Vmware).
What is the suggested best setup of these discs? I have been using raid10, but unsure if this is the best.
If reliability is your prime requirement, you'll want RAID6 (or if using ZFS, RAIDZ3 or RAIDZ2), which allows any two (3 with RAIDZ3) drives to fail without data loss. However, capacity will suffer and performance even more.
If you want performance, RAID10 will usually be the fastest (this does depend on your IO model). You lose half the capacity of your disks, and you can only guarantee data integrity with the loss of a single disk (it's possible multiple disks fail without losing data, not guaranteed).
If you want capacity, RAID0 will have the most. It will also increase the chances of data loss; approximately 6 times since you have 6 disks. Performance will be high, though there will be situations where RAID10 is faster, primarily in read operations.
Note that RAID5 did not appear in any of the above as it is a compromise between all of the above. It is most useful when you don't need any of the above in particular, but want at least some of all of them.
Raid 10 will give the best performance whilst also having resilience against a failure. The down side is that the total usable space will only be 50% of the total i.e. 3 x 74.8
If performance is not an issue then you could go for RAID5 which will give you 5 x 74.8.
RAID6 is also an option but with only 6 disks, probably not worth it compared to RAID10 as you only gain a small amount of extra usable space at the expense of much slower performance
So in summary I'd go for RAID10 for performance otherwise RAID5
Just the one virtual host? Or do you mean you're running lots of virtual machines on this box?
Without knowing a lot more about what you are trying to achieve, we don't either.
The right answer depends on what the boxes will be doing - streaming large media files? File serving? HTTP serving? Do you want to try to isolate the I/O from each VM or optimize throughput across them all or get the most storage capacity from the disks?
ZFS provides a good mixture of those features, here are FREE ZFS Options:
(New users have limits on Links posted so change hxxp to correct letters)
You have "IBM xSeries with 6x SAS 74.8GB 10K" so put out the bucks for a decent RAID Controller.
Use Google to find info on the features offered by each RAID Level, here is one great hit: http://www.supermicro.com/manuals/other/MegaRAID_SAS_Software_Rev_I_UG.pdf