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Topic: HD Allocation Unit Size

  1. #1

    HD Allocation Unit Size

    Hey Everyone,

    I just completely rebuilt my system from scratch and have a RAID Array just waiting to be formatted and wanted some opinions. It is 220GB in size and I primarily want to use it for my sound libraries from vienna and GS3 and also for my recordings and mixdowns. What size allocation would you use on this? Am going with NTFS for file system. I have read a lot of places saying that perhaps for video and audio we should use the largest (64K) for this. Just wanted to know from experienced peeps what has proven to be better.

    options are:
    512, 1024, 2048,4096, 8192, 16K, 32K and 64K.


  2. #2

    Re: HD Allocation Unit Size

    Well since no one answered I went with my gut on this one and it was right. I went from the XP default of 4096 to 64K. My lord what a difference for my samples drive. I recommend this to anyone who is trying to decide for their sample drives. I still believe the xp default or 4096 is best for your system though since it's full of smaller files.

    Hope this helps someone!!

  3. #3

    Re: HD Allocation Unit Size

    yeah, thanks maestro.

    I'm about to format aswell, and had no idea, that would change anything.

    Is there anyway you can elaborate on how the performance is better?



  4. #4

    Re: HD Allocation Unit Size

    I sure can.

    What happens is when you format a disk the drive gets segmented into specific size chunk. The best way to look at it is to picture a storage facility in your head. You go there and you see building upon building of exactly the same size looking units to rent. When you format your drive this happens to the surface. So now imagine this. You have a storage compartment the size of a garage(64K) and right next to it you have one the size of a little dog house(4K). Before you jump to conclusions here you need to understand one thing. What you are really telling windows is to write data to the HD in a certain size. So if you told windows to use the garage size for allocation that means that it will say ok i have 120gb of HD space and all my blocks will be written 64K in size even if the file is only 1k it will use the whole 64K up wasting the space. So you have to think ok my System drive should use the dog house (4K) allocation size because i have tons of little files and dont want to waste space. My samples drive however i want to use the Garage (64K) size units because i am dealing with huge files and it wont waste space anyways. Plus i need it to be read back to me as fast as possible with the least ammount of proceessing and I/O requests.

    So then you say yes but this doesn't answer my question about performance. Ok knowing this here goes.

    lets say you format a drive with default (4K) NTFS. You store a file that is 250MB (bosendorfer 290 or something equivalent). Now what happens is you tell the system i need you to read to me that information and stream it while im playing it back. This means the computer can process only 4K of data per I/O request. The computer says, ok no problem. Each time you need something your computer uses an I/O request to get it processed. So what does this look like in math? First of here are numbers you need for the formula:

    1024 bytes = 1K
    1024 Kbytes = 1MB

    With that 250MB file it would do this.

    HD Allocation size = 4096 or 4K
    File Size is = 250MB or 256,000K
    Total Number of I/O's to process this request: 256,000K / 4K = 64,000 I/O's

    What if it you had formatted it at 64K?

    HD Allocation size = 64K
    File Size = 250MB or 256,000K
    Total Number of I/O's to process this request: 256,000 / 64K = 4,000 I/O's

    You can clearly see that Formatting your systmem with the largest 64K value is the best way for your samples drives. Because what that is really saying is ok the Data is on my drive and I can read back 64K of data per I/O instead of only 4K saving the computer a heck of a lot of resources and super speeding up your processing and requests as well as latency.

    Hope this helps!

  5. #5

    Re: HD Allocation Unit Size

    Wow, thanks man. I guess I'll just have to try it to see!

    I wonder if I can convert the drive without formating it??

    thanks man!


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