Hello List Members (and Holiday greetings!)
This rambles a bit ... my apologies in advance.
I am in the process of building a large CentOS-based VM host machine which will replace several individual boxes. I've done the usual hardware research and ended up with a SuperMicro motherboard, dual Xeons, lots of ECC RAM, solid power supply, and tons of cooling.
When it comes to the best disk array layout for 7 guest instances of CentOS (mostly 64-bit) I run into the classical argument of disk I/O performance versus array robustness. I'm using Linux software RAID so I don't get locked into a vendor's controller, and because I've got CPU cycles to burn.
The intent is to use CentOS-6 with KVM after climbing the usual experimental learning curve. I've got years of CentOS experience, but none with KVM.
So, underneath all of this I could use RAID-10/RAID-6/RAID-60. Which one is better for the following work mix:
- 4 web servers, not heavily loaded (yet), mostly CGI. - 2 independent Zimbra email servers, which seem to spend most of their time rejecting spam and malware. - A primarily-inbound FTP server with bandwidth throttling. - A batch ImageMagick video process which kicks in a couple of times/day for a few minutes. - A secondary/backup SMB server, not heavily used. - A very lightly loaded DDNS server.
Two spindles will be used in RAID-1 for the host OS filesystems.
I have 10 large drives for the guest machines, but because they're 2 TByte I want to ensure reasonable fault tolerance, meaning the ability to handle at least two drive failures. This really means that an array rebuild to replace *one* drive stands a good chance of succeeding.
At first glance this would seem to be a system which will be doing more reads than writes, so RAID-6 or 60 might be a reasonable fit. RAID-10 offers much better write performance according to what I've been reading, but is less fault tolerant. RAID-60 is a bit of an unknown to me with regard to performance.
In case you're wondering, I don't consider RAID to be a backup, so all of this will be automatically backed up to duplicate separate machines, each having tons of RAID-6 storage. Each individual guest OS will do its own rsync thing.
Please forgive my lack of VM experience, but an additional question ...
I'm thinking of creating a separate RAID-xx MD partition for each guest. Should I hand each over as a 'device' to KVM or is it better to place the guest filesystems in a big file on each separate MD partition? Or, is it better to create one huge RAID-xx partition and just use big filesystems-in-a-file. Either way would probably take the same amount of time (long!) to rebuild an array, if I understand this correctly.
The collective wisdom of this list is most welcome.
Thanks muchly, Chuck