[blackmacx]

Hi,

I am looking to reformat my HDD (20GB) and want to drop my block allocation size from OS X's default of 4K to .5K; what I need to know is what is the best application to do this (I have FWB HDT and SpeedTools from Intech; but neither will allow me to reformat and also redefine the block allocation size). I have heard about Lacie's Silverlining application (used it under OS 9 a couple of years ago, but left it due to repeated problems with it's formatting and stability). Therefore does anyone have any suggestions?

Cheers,

BlackMacX

[bradoesch]

I'm pretty sure that pdisk will let you use 512 KB blocks.

[someone_else]

Originally posted by blackmacx:
Hi,

I am looking to reformat my HDD (20GB) and want to drop my block allocation size from OS X's default of 4K to .5K; what I need to know is what is the best application to do this (I have FWB HDT and SpeedTools from Intech; but neither will allow me to reformat and also redefine the block allocation size). I have heard about Lacie's Silverlining application (used it under OS 9 a couple of years ago, but left it due to repeated problems with it's formatting and stability). Therefore does anyone have any suggestions?

Cheers,

BlackMacX

Don't do this unless you have a very good reason to. The best alloc. size is 4K because that matches the VM system page size of 4K. Since these match, disk txfr's are optimized. By lowering the block size, you will cause many more disk txfrs and may even cause the VM system to loose some performance.

[tooki]

Reducing block size can significantly impact disk performance, increase fragmentation, and increase system memory usage (since the memory map for 0.5K blocks is 8 times as large as the map for 4K blocks).

Unless you have a very specific need to do this, don't. Just use the default.

tooki

[Person Man]

Originally posted by bradoesch:
I'm pretty sure that pdisk will let you use 512 KB blocks.

No, it won't. I just looked at the man pages for both pdisk and fdisk, and neither one mentions allocation block size.

[Prijker]

Don't do this unless you have a very good reason to. The best alloc. size is 4K because that matches the VM system page size of 4K. Since these match, disk txfr's are optimized. By lowering the block size, you will cause many more disk txfrs and may even cause the VM system to loose some performance.

Reducing block size can significantly impact disk performance, increase fragmentation, and increase system memory usage (since the memory map for 0.5K blocks is 8 times as large as the map for 4K blocks).

So, does it mean that, say, an 8K alloc. size will double VM system page performance and produce half fragmentation and memory usage?

Vic

[bewebste]

Originally posted by Prijker:
So, does it mean that, say, an 8K alloc. size will double VM system page performance and produce half fragmentation and memory usage?

Hehe, unfortunately not. You get the best performance when the VM page size is equal to the block allocation size. If the blocks are smaller, that leads to more reads and potential fragmentation. If the blocks are too big, then you can often read more data than is needed and fill up memory, since you have to read at least 8K even if you only need 4K.

[Prijker]

So, does it mean that, say, an 8K alloc. size will double VM system page performance and produce half fragmentation and memory usage?

Hehe, unfortunately not. You get the best performance when the VM page size is equal to the block allocation size. If the blocks are smaller, that leads to more reads and potential fragmentation. If the blocks are too big, then you can often read more data than is needed and fill up memory, since you have to read at least 8K even if you only need 4K.

mmm, so, the best solution would be to increase the VM page size itself?

[Gul Banana]

Depends. Why is it that you want to do this in the first place?