On Wed 23 Feb, 2000, "Bruce Sterling Woodcock" sirbruce@ix.netcom.com wrote:
The article doesn't say, but bigger, faster disk drives often draw more power. Thus, NetApp needs to have shelves that can support them first, before they can test them for reliability. There are a lot of issues involving mechanical vibration and so on that have to be assessed before such a drive could be qualified. It may be that this particular drive is not appropriate for certain shelves.
Well, yeah, so much so obvious. So how soon was that? 8)
More spindles is better performance, if you are read-heavy. If your filer seems slow and it's reading constantly but the CPU is still under 100%, more spindles could help.
So much for conventional wisdom. However, my question was trying to elicit something a little more, well, complete as a model of performance.
I mean FCAL is a loop technology, and filers can come with 1, 2 or 3 loops. How much does performance differ when using 1 chain as opposed to 3 balanced chains, using which drives, using what RAID set sizes and volume mappings? How does performance get affected by the size of the disks you use?
See, if none of these things makes any difference to performance I'd love to know why. If they *do* then I'd love to know how to build faster filers.
I'd be happy with an analytical model, or a set of tables taken from either real lab testing with real filers, or simulator results. As it stands though, all we have are rules of thumb that sound plausible.
The same goes for backup performance. There's been so much discussion on the list about both topics, but I can't honestly hand-on-heart tell someone how best to set-up their filers. I'd write something if I knew the answers myself.
The best I can find is things like: http://now.netapp.com/NOW/knowledge/contents/FAQ/FAQ_560.shtml
I've been meaning to brush up on queueing theory so maybe I *will* try to work something up myself on this. I'd just hate to reinvent the wheel if someone's done it already. I also don't know anything about the buffers in the filer, on FCAL interfaces, the network interfaces, the precise use of the WAFL, etc.. So my model might be under-informed.
Here's a thought to mull over: if you have 20 18 gig drives on 2 loops and 16MB nvram, will you see better or worse performance than with 40 9GB drives on 1 loop with 16MB nvram presuming your clients are all writing as fast as they are allowed? Please disregard any "such configs aren't shipped" objections as this is an in-principle hypothetical. Please do consider the effect of RAID sets, and incremental disk-additions over the lifetime of the filer in question. I picked writing as the task because I wanted to point out also that there's an impact on the DOT algorithms, based on the spindles, the RAID set sizes, and maybe the chains too.
I don't know the answer, but I'd like to. Without such models we all have to purchase filers somewhat in the dark, and either pray that we got it right, or expend more time than we could in evaluating our purchases for suitability.
One question - is anyone else interested in this or am I just shooting my mouth off needlessly?
-- End of excerpt from "Bruce Sterling Woodcock"