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NTFS Allocation size for formatting


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#1 RevGAM

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Posted 02 May 2012 - 04:04 PM

I'm going to reformat a 111GB HDD with NTFS, and I was wondering if there are any problems that will occur if I decrease the allocation size from the default of 4KB to something smaller. Please advise. Thanks!

BTW, I'm using WXP SP3.

Edited by RevGAM, 02 May 2012 - 04:05 PM.

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#2 Platypus

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Posted 02 May 2012 - 09:34 PM

4KB is the optimum for NTFS, so performance will be reduced with smaller allocation units, the MFT will be larger. I think 4KB is also required for some enhancement functions like NTFS compression, and load optimization for executables which requires the file system to have the same cluster size as the RAM page allocation. I'm not sure if the performance of the paging file specifically is affected for the same reason.
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#3 RevGAM

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Posted 02 May 2012 - 11:02 PM

So, I'll lose some functionality and speed, right? Will it destabilize the system, too? How critical is compression on the Windows partition anyways since I don't use it much?

Namaste, Peace & Love,
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#4 Platypus

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Posted 03 May 2012 - 08:19 AM

Hmm, actually it's a maximum of 4KB cluster size to allow the use of NTFS compression, so that functionality will not be lost by using smaller allocation units. I've only found any reason to change to larger clusters, for better write performance, so I recalled that as preventing NTFS compression (and also use of most defragmenters).

The allocation unit size is transparent to the OS and applications, and there will be no reason for there to be any ill effect on system stability. As the cluster size reduces, the number of I/O transactions per volume of data will increase, so performance will fall away, 512 byte allocation units being the worst.

I can't think of any benefit for having small cluster size on a large volume, unless enormous numbers of very small files were being stored. Is this the type of situation leading you to consider small clusters?
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#5 RevGAM

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Posted 03 May 2012 - 10:35 AM

No, I don't have a lot of small files, unless you count "read me" files. ;) Mostly, I just like to know my options and, in the case of this old machine and the high I/O volume, it seems best to stick to the 4KB default.

Thanks, and I love the moniker! :)

Namaste, Peace & Love,
Glenn


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#6 RevGAM

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Posted 03 May 2012 - 10:39 AM

Actually, there was one consideration:
More file sizes are divisible by 1 or 2 than 4 KB, therefore fewer kilobytes would be wasted with a smaller allocation size.

What I mean is, if your file is 16 KB, then there's no wasted space. But, if it's 13 KB, then you've wasted 3 KB. If there are lots of files that aren't evenly divisible by 4 KB, that can amount to MB of lost space. I'm not so great at maths, but I suppose that, theoretically, you could lose a gigabyte of space that way on a very large drive (I have a 1 TB portable that I'm thinking of).

Also, I'm wondering if the allocation size affects how many GB of available space there will be on the drive after formatting. For example, my 111 GB HDD is actually 120 GB - the balance being lost to formatting, the MBR, etc. If I were to use a smaller allocation size, perhaps I'd get 112GB. I fill up HDDs very quickly with my library of software, music, photos and videos. :) Given that my dead laptop had rather more space on the HDD than this machine, and I had used up almost all of the space on it before it died, I'm sure I'll have the same problem with this one.

Edited by RevGAM, 03 May 2012 - 10:46 AM.

Namaste, Peace & Love,
Glenn


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#7 Platypus

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Posted 04 May 2012 - 06:02 AM

Yes, you're contemplating "slack space", the inevitable unused portion of the final cluster in each file that isn't an exact multiple of the cluster size. File sizes normally vary randomly, so the average lost space will be the number of files multiplied by half the cluster size.

So the default 4KB wastes 2MB per thousand files, and using 2KB clusters would recover 1MB per thousand. You'd need to store a million files on your 1TB volume (1MB average file size) to gain around 1GB by doing this, but you'd lose some of this to the extra space taken to save the records of twice as many clusters. IMO this wouldn't be significant enough to justify, even less so if videos & the like take the average file size higher.

Some reading did bring to light another quoted potential disadvantage of smaller clusters. Where files are "grown" over time, like databases, the larger the cluster size, the less potential for fragmentation, so smaller cluster size can theoretically increase fragmentation. I doubt if this is going to be significant these days as it applies if the data written is significantly smaller than the cluster size. I think modern data sets should be bloated enough to swamp the effect.
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#8 RevGAM

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Posted 04 May 2012 - 06:49 AM

I don't remember the exact count, but I definitely have a large number of files. Once I recover the laptop data, I'll be able to say how many.

How many millions of files would justify a 1 KB or a 2 KB allocation size, in your opinion?

I'd only be worried about fragmentation in the case of things like frequently updated databases as opposed to static files. Aside from AV databases, I'm not sure how many other database files there are in Windows, let alone other programs I use.

Namaste, Peace & Love,
Glenn


If I have frustrated you, then I must be a student. If I've imparted information or a skill to you, then I must be a teacher. If I've helped you, then I must be a volunteer. If I've touched your life, then I must be happy!
If you had to choose between saving just your family, or saving 10,000 GOOD people (but not your family), what would you choose?





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