Advice on partition alignment with SSDs

graysky · 2010-06-27 09:36:48

I am ready to buy an SSD and have narrowed it down to either the OCZ Vertex 2 or Intel X25-M. I found two different suggestions regarding the proper way to align partitions on an SSD.

Ted Tso and others recommend using 224/56 option while others advocate the 32/32 option:

# fdisk -H 224 -S 56 /dev/sdX

Or

# fdisk -H 32 -S 32 /dev/sdX

I have updated the SSD wiki page with these (and other) info but would like some feedback from folks in the Arch community who are actually running an SSD-based Arch system.

How did you align your partitions?

Last edited by graysky (2010-06-27 10:27:32)

Nepherte · 2010-06-27 10:07:28

It depends on what the erase block size is for the ssd. For a X25-M, the erase block size is 512KB (I've seen people claim it's 128 but I don't think that's correct, and 512 is a multiple of 128 so there's no harm).

When using 32/32 you get a cylinder size of 32*32=1024 bytes and since fdisk partitions in units of 512 cylinders, you get 1024*512 = 512KB, exactly the erase block size! When you create partitions, they will be aligned. You could also use other values for S/H like 8/128, 16/64, it will ultimately give you the same result: your partitions will be aligned.

The 2 most useful pages I've found about aligning are:
http://www.nuclex.org/blog/personal/80- … d-on-linux
http://www.ocztechnologyforum.com/forum … stcount=98

In conclusion, the S/H values depend on ssd's erase block size and are not randomly chosen.

Last edited by Nepherte (2010-06-27 10:09:54)

graysky · 2010-06-27 10:25:48

Thanks for the post. So for an EBS of 512 KB you're recommending the 32x32=1024 option. I don't understand how Ted's 224x56 option works... since that product is 12544.

Last edited by graysky (2010-06-27 10:27:15)

Nepherte · 2010-06-27 12:35:15

Then you're not alone. I don't understand his H/S choice either but in the end it's still a multiple of 128 (his EBS). Somewhere in his post he gives some sort of explanation:

you need to align partitions on at least 128k boundaries for maximum efficiency. The best way to do this that I've found is to use 224 (32*7) heads and 56 (8*7) sectors/track. This results in 12544 (or 256*49) sectors/cylinder, so that each cylinder is 49*128k.

32/32 is just easy to remember. You can find a whole table of combinations here:
http://www.ocztechnologyforum.com/forum … post373224

Arch Linux

#1 2010-06-27 09:36:48

Advice on partition alignment with SSDs

#2 2010-06-27 10:07:28

Re: Advice on partition alignment with SSDs

#3 2010-06-27 10:25:48

Re: Advice on partition alignment with SSDs

#4 2010-06-27 12:35:15

Re: Advice on partition alignment with SSDs

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