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disk io size 4k-512k

Posted on 2013-01-22
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Last Modified: 2013-02-08
i wanted to determine which disk io block size to go with and I am note sure which option is best?  choice range from 4k to 512k? what are the pros and cons?  i have a 2012 server.
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Question by:Kylo Ren
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BlueCompute earned 1600 total points
ID: 38807777
In general, larger clusters improve performance at the cost of wasted space. The best size depends on the average size of the files you will be storing on the volume - I've found 16 or 32KB to be a reasonable choice on a window server, but it depends on usage - unless you're trying to make a particularly high-performance environment I wouldn't worry about it too much. The default figures can be found here:
http://support.microsoft.com/kb/140365?wa=wsignin1.0
and some information about he performance impacts here:
http://technet.microsoft.com/en-us/library/cc767961.aspx
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by:Kylo Ren
ID: 38866460
ok space may not be that important to me. how much is actually wasted? i just need a rough idea to see what trade off would be.

lets say i have a 500gb volume and i want the best performance (largest cluster size).  how much space can i expect to lose? also are there any other downsides to having a large cluster besides wasted space?

thanks a lot
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by:Gerald Connolly
Gerald Connolly earned 400 total points
ID: 38867163
well if you have lots and lots of small files, you will waste a lot of space, all it needs is one byte used to waste all the remaining space in a cluster
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by:BlueCompute
ID: 38868090
Basically, the cluster size is the smallest amount of data the file system will allocate. If your file is smaller than this, any extra space is wasted. For a demonstration, create a new text file on your local hard drive, enter 1 character of data and look at the file properties. You'll see the following:

Size: 1 bytes (1 bytes)
Size on Disk: 4.00 KB (4,096 bytes)

This is with a 4k cluster size. The average file size in my current Win7 windows directory is 165KB, but that's a mean average. With a 4k cluster size, I get

Size: 16,771,835,355 bytes
Size on disk: 16,965,893,594 bytes

Which is very little wastage, as most files are >4k in size anyway. To be honest, it really isn't likely to make too much difference to performance or disk usage unless you start going to very large clusters, which doesn't make sense unless you're only dealing with large/fixed size files.
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