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I guess that this is an old question, but all answers I found on the net was very diverted, so here goes...

I need a dedicated volume for tens of thousands of ~10MiB and ~50MiB files. I suspect that a large NTFS cluster size will speed up the file server, but will a large cluster size do any other harm like slow things down, or waste lots of space?

Should i use 64K clusters, 32K or just plain default (4K size)?

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up vote 2 down vote accepted

To my knowledge, NTFS itself does not have any performance problems associated with larger cluster sizes.

If you're really looking to eek out all the speed you can, I'd recommend simulation and benchmarking. How your application reads data (4K blocks, 8K blocks, etc) is going to make a difference, as is the cache hit pattern on the NT cache and the underlying RAID cache. The disk / storage hardware (RAID layout, SAN configuration, etc) is going to make a difference, too.

Ultimately, the behavior of the application is going to be the biggest dictator of performance. You see "planning guides" for various applications (Exchange, SQL Server, etc) out on the 'net. All of the serious ones are based on real-world benchmarking with load simulation. You can write "rules of thumb", but with any given system there may be quirks in implementation at lower levels that turn rules of thumb on their ear.

If your application is suited to simulated work, spin up a simulated corpus of files and simulate a workload on them, using various filesystem / RAID / disk configurations. That's going to be the only way to know for sure.

(Aside: Does anybody else find it funny to hear a 10MB file called "small"? God, I'm old...)

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Hehe.. I know how you feel, (re: small files). We've got an atmospheric modeling group here that utilizes a 14Tb array on my SAN. The files that they refer to as "small" are around 241 Mb in size and those comprise the raw data that they begin with. – Greg Meehan Jun 17 '09 at 14:54
10MB was half the size of the first PC our family had. No easy answer for my question? I guess I'll have to do some benchmarks then. – Bård Jun 17 '09 at 18:12
You really will have the best luck if you do some benchmarking and simulation. If you're using a COTS application try and talk to the manufacturer about it. If it's custom, then it's "all you". smile Yeah-- my first PC with a hard drive had 40MB of storage (the old ST251). My first computer, though, used audio tape storage. – Evan Anderson Jun 17 '09 at 18:38

Easy answer: If the majority of your files will be 10MB or more then I'd recommend you use as large a cluster size as possible, but this may be a little wasteful space-wise.

Complex answer: You should analyse your disk's cache, your disk controller's cache, your OS's cache and the actual files and their sizes. This will be better, but harder to get right.

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If the average file uses 32K cluster (half of 64K) and I have 100000 files then it means that I use about 3 GB in waste. I think I can live with that. – Bård Jun 17 '09 at 18:08
Good point, well made! – Chopper3 Jun 17 '09 at 19:30

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