20TB Storage System
tlambert2 at mindspring.com
Fri Sep 5 22:04:57 PDT 2003
David Gilbert wrote:
> >>>>> "Poul-Henning" == Poul-Henning Kamp <phk at phk.freebsd.dk> writes:
> Poul-Henning> I am not sure I would advocate 64k blocks yet.
> Poul-Henning> I tend to stick with 32k block, 4k fragment myself.
> That reminds me... has anyone thought of designing the system to have
> more than 8 frags per block? Increasingly, for large file
> performance, we're pushing up the block size dramatically. This is
> with the assumption that large disks will contain large files.
My assumptions on the previous two statements by Poul are:
1) You cannot trust that a short will be treated as an
unsigned 16 bit value in all cases, so values that
are between 32768 and 65535 may be treated incorrectly.
2) A fully populate block bitmap byte, which means a divide
by 8, is necessary to avoid potential division errors.
In other words, he's afraid that the sign bit and/or the block
size bitmap used by frags may be treated incorrectly.
I have to agree with both those observations. A number of people
have, historically, reported issues with a divisor other than 8,
and the worry about the sign bit is common sense, given the many
historical issues faced by other OS's when it comes to 64K block
More information about the freebsd-performance