From what I have read on this matter, it all depends on what you are intending
to use your RAID array for. If you plan on doing most large file size transfers
such as with audio/video, then you should make the chunk size large. If you
plan on doing mostly small file size transfers such as maybe with a web server,
then use a small chunk size. If you plan on doing a mixture of both large and
small file size transfers, then choose something in the middle.
From what I recall reading, a RAID controller transfers complete blocks of data
to or from the RAID set (commonly called chunks). If you make your chunk size
large, oh say like 256KB, and you only transfer a 5KB file the whole chunk most
still be read from and written to the array. This would waste time because the
RAID controller must first retrieve the data and then write it back to the
array. The opposite end of the spectrum would also make you loose some time if
you made your chunk size 16KB and you needed to write a 200MB .avi file to the
drive since the RAID controller would need to access 16x as many blocks than if
you set it up for 256KB chunk size.
The chunk size is not to be confused with cluster size since that is what the
file system looks at as the smallest block to transfer. I try and use this as my
rule-of-thumb:
Mostly small files=16KB to 32KB chunk size
Mixture of large and small=32KB to 64KB chunk size
Mostly large files=64KB to 128KB chunk size (256KB if the controller supports
it--mine doesn't)
Paul
