Re: device and partition alignment

Dear Stefan,

In message [ref] you wrote:

I guess you couldn't find much about this as it has more to do with
common sense than magic formulae.  If you have 4k-sector drives, align
everything at multiples of 4k, use filesystem-units of multiples of 4k.
 As I read and it also seems very logical from the ATA / SCSI point of
view, a stripe size of 256k seems most straight forward.  This is the
largest amount of data (a.t.m.) that can be read or written with a
single command to a disk.

And why would that be optimal, in general?

For example, in a file system I have here (with some 15 millions
files) we see the following distribution of file sizes:

	65%   are smaller than  4 kB
	80%   are smaller than  8 kB
	90%   are smaller than 16 kB
	96%   are smaller than 32 kB
	98.4% are smaller than 64 kB 

With many write accesses going on, a stripe size of 16 KiB gives much
better performance.

I think you cannot recommend a stripe size or other specific tuning
measures without exactly knowing the characteristics of the load.

Best regards,

Wolfgang Denk

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