some questions 16 disk 15k SAS build for VMs

[Makje]

For a client i'm investigating a KVM or ESXi setup with 3 nodes and a SAN. A relatively budget SAN based on Freenas and ZFS.
(haven't decided on NFS or iSCSI yet, NFS is more flexible but iSCSI has slightly better write speeds)
It wil be hosting 7 VMs of which 5 windows server 2008 (AD, Exchange, SQL, 2x variuos applications) and 2 linux (webserver, Elastix VOIP)
KVM isn't the best for windows virtualization, but it is what i know best (but always had it with local storage)

Anyway i've been reading a lot about ZFS and Freenas and have come to the following setup for a SAN:

16x 15k 300GB SAS disk 2,5 inch
2x IBM M1015
2x Intel 320 SSD 80GB MLC mirrored for SLOG (4 GB partition, the rest unused)
SuperMicro X9SRi-3F socket 2011
Intel Xeon E5-2630 (6-core 2.3 Ghz)
64GB RAM (4x 16GB, still 4 slots unused)
HP NC364T Quad Port Gigabit NIC (intel)

My questions then:

with 64 GB RAM, will i still really profit from a L2ARC SSD? (Intel 320 160GB or something?)
What if i up the memory to 128 GB?

Is the SLOG perhaps unnecessary for only 7 VMs? (it will probably grow to 10 or perhaps 15 VMs in time)
Or is a Intel 313 SSD a better choice? it's a 20 GB SLC drive, but does not have "Enhanced Power Loss Data Protection" (to preserve data in case of powerloss if i understand correctly)

For the SAS disks would 2,5 inch or 3,5 inch SAS make a difference? 3,5 inch SAS disks are considerably cheaper (145 versus 255 euro each)
Would a pool of 8 mirrors be best for IOPS, or 2 RAIDZ2 arrays? The latter seems safer in that 2 disks in 1 array may fail without direct data loss.

The Supermicro motherboard has a 8x SAS SCU onboard, i can't find out much about it. Can i use it for ZFS?
It also has a new Intel C606 chipset, is it supported by the latest FreeNAS?

Is the processor perhaps too much?

I hope someone can help me out, i can't really justify buying the stuff just to test if it wil work

 

[starryganesh]

There's no difference between 2.5" and 3.5" SAS drives other than form factor, so you might as well get the bigger ones and save some money. The rest of the questions I'm not sure about, sorry.

 

[louisk]

The ram will help, as long as the data set (size of your VMs) will fit. I'd your VMs are more than 64/128G, it won't be able to keep them in ram. In this situation, l2arc is handy. I'd probably start with 64g ram and get SSD big enough for 1.5x your active vm size. Meaning, if your only going to have 2 VMs running and together they are 100G, I'd put 150G of l2arc in. Don't count the space consumed by VMs that won't be running most of the time.

For calculating the iops, you should try to measure the iops of a similarly loaded system running the same OS. I don't know how to do it for windows, Linux can run vmstat. I'd run that every 5m for 36hrs of "normal" activity. Then you can crunch the numbers and figure out how many iops you need. This will in turn dictate what kind of spindles and redundancy you need.

If you are looking for performance, you will want striped mirrors. Biggest performance. If you are concerned about replicas, use a three or four way mirror.
If you really want good performance for your SQL Server, get some flash storage and store them on that. The biggest problem for your DB is likely to be IOPS. I believe you can to some extent control storage resources from something similar to a resource group, but I don't remember and don't have access to a system just now.

For CPU performance, if you want good VM performance, use the same number of virtual CPUs as you have physical cores. You can use resource pools to control the resources assigned to groups of servers. For example, you could have a group of servers that need 70% of the CPU resources, so you assign that group 70%, the other group (no matter how many servers are in it) get what ever is not being used (could be 30%, could be more, depending on what all is running).

 

[paleoN]

There's no difference between 2.5" and 3.5" SAS drives other than form factor, so you might as well get the bigger ones and save some money.

Seek times, smaller diameter == faster seek.

If you are looking for performance, you will want striped mirrors. Biggest performance. If you are concerned about replicas, use a three or four way mirror.

IMO, four-way mirrors are rather excessive. Double-parity is sufficient.

If you really want good performance for your SQL Server, get some flash storage and store them on that. The biggest problem for your DB is likely to be IOPS.

+ 1. In fact if you're looking at 15K SAS drives I would consider a pure SSD based pool.