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SANs and Excessive Disk Utilization?
pnutjam asks: "I work for a small to medium mental health company as the Network Administrator. While I think a SAN is a bit of overkill for our dozen servers, it was here when I got here. We currently boot 7 servers from our SAN, which houses all of their disks. Several of them have started to show excessive disk load, notably our SQL server, and our old domain controller (which is also the file/print server). I am in the process of separating our file/print server from our domain controller, but right now I get excessive disk load during the morning when people log on (we use roaming profiles). I think the disks need to be defragged, but should this be done on the servers, or on the SAN itself? When it comes to improving performance, I get conflicting answers when I inquire whether I would get better throughput from newer fibre-channel cards (ours are PCI-x, PCI-e is significantly faster), or mixing in some local disks, or using multiple fibre channel cards. Has anyone dealt with a similar situation or has some expertise in this area?"
I am the Sr. Storage Architect for a Fortune 100 company. If you gave the type of array you have specifically, I'd be able to give more specific advice. That said: 1. You should have at least two fibre cards in each box anyway, and it has nothing to do with throughput. 2. Generally, your bottleneck is the disks themselves. If you want to increase performance, You need to increase the number of spindles that the data is striped across. Depending on the type of array, this may be a non-disruptive operation. The other big thing to look at is the type of RAID being used. You can usually get better performance from something striped with RAID10 vs. Raid 5, especially for write intensive data, because RAID 5 incurs an IO write penalty in calculating parity. 3. If you are going to defrag, do it on the server. It could help. There are some defrag functions available in most mid tier storage arrays, but it isn't what you think. The defrag there typically refers to lining up LUNs in a raid group. So, if you have a raid group with 5 LUNs in it, then delete one, you end up with a big empty space in the middle of the group. Defragging that raid group lines up all the LUNs inside that raid group.