SAN Disk Speeds
I'm looking at buying a SAN for a virtualisation project - the Dell analysis tool recommends 10k disks for our current usage, but I'm wondering if I should look at 15k?
The SAN(s) will be used to serve up 20 servers (Including the fileservers) to 3 nodes for 500 Clients
Network wise I'm looking at iSCSI (Dual Controllers on the SAN, 4 connections at 1GBs each).
Thanks in advance, Ben
if your buget will allow for faster disks then you should always use them.
How many disks does the SAN take? 24 10k disks will be much faster than 8 15k disks for example.
Especially with you wanting it to be a FS I would recommend as many 15k disks as will fit.
I'd say - it depends.
Depending on what you are going to be running, you may want (need) to tier your storage, you may want to have a mix of fast 15k for VM's and large 7200RPM / 10K SAS for Filestorage server by the VM's depending on how critical the read/write speed needs to be.
We've supplied ISCSI San's for lots of businesses / uni's so if you want to have a chat about some alternative options to a Dell offering, let me know.
Forgot to mention. Spec'ed up at the minute are 12 900GB 10K SAS 6Gbps Disks!
As above depends on the usage... if it's a server doing roaming profiles and lots of ever changing documents then get the fast disks on the case, especially if you've got hundreds of users logging in at once and hammer the profile server.
If it's a shared drive resource server then you'll need capacity over speed, at this point 2TB NL-SAS \ SATA will be more effective. If you're virtualising the file servers the handy part is that you can separate out the file servers to match their role and store them on specific sets of disks matched to performance needs :)
We run 10 x 15k disks at the moment on our EMC VNXe, that does file servers, SQL and a couple of others but YMMV dependent on number of users etc. Also are those disks 2.5" or 3.5"? The smaller drives give less IOPS but you can pack more of them into the SAN chassis.
Also have you run a capacity planning tool on your current servers? You really need to do that to get your current disk IOPS requirement from your existing servers before you can have any idea what you'll need on virtual. The VMWare planner is very detailed but you'll need a partner to run it for you. As an alternative you can run perfmon over a period of days to get an idea but to do it for 20 odd servers and collate the info is more aggro than its worth imo, get the company you're going to buy the kit from to do it as part of the tender.
Have you considered RAID levels? With virtualisation and the multimedia content/large profiles/etc going on on fileservers you need to choose your RAID level appropriately. Most people say RAID 10 for virtual drives and RAID 5/6 for files. However, I have found RAID 5 is not good enough for our school. All our files/profiles/apps are stored on 2 servers, one with 12 x 10k SAS and the other with 12 x 15k SAS, both in RAID 10. For 400 concurrent users we are pushing the disk IO to it's limit.
Disk IO is by far the biggest bottleneck in computer performance. Buying the wrong disks now will cost you a fortune to replace in the future. Buy the best you can now.