extra I/O at the start of disk zone test?

With the following job description

[global]

bs=1k

direct=1

rw=read

ioengine=libaio

iodepth=2

zonesize=1k

zoneskip=1023k

write_bw_log

[/dev/cciss/c0d1]

write_iolog=foo2

The idea here is that I wanted to line up my zones to start at 1M
boundaries across the disk by writing 1k and skipping the next 1023k.
In practice I don't get the alignment because of an extra initial I/O.
I get an iolog that looks like

# head foo2

fio version 2 iolog

/dev/cciss/c0d1 add

/dev/cciss/c0d1 open

/dev/cciss/c0d1 read 0 1024

/dev/cciss/c0d1 read 1024 1024

/dev/cciss/c0d1 read 1049600 1024

/dev/cciss/c0d1 read 2098176 1024

There's a read that I don't expect in that log, namely the read starting
at byte 1024. Because that read is there, the disk zones get offset by
one block. I expected output like

# head foo2

fio version 2 iolog

/dev/cciss/c0d1 add

/dev/cciss/c0d1 open

/dev/cciss/c0d1 read 0 1024

/dev/cciss/c0d1 read 1048576 1024

/dev/cciss/c0d1 read 2097152 1024

/dev/cciss/c0d1 read 3145728 1024

Where the zones are all aligned to 1m boundaries. I can get what I want
with specifying "offset=1023k" which effectively puts the I/O for the
first zone at the end of that zone which isn't great, but it does give
me aligned zones.

# head foo2

fio version 2 iolog

/dev/cciss/c0d1 add

/dev/cciss/c0d1 open

/dev/cciss/c0d1 read 1047552 1024

/dev/cciss/c0d1 read 1048576 1024

/dev/cciss/c0d1 read 2097152 1024

Is this the expected behavior? Am I just not getting the point of
zonesize/zonefile or is this a bug?

Thanks,

Ryan

BTW: I'm using fio version 1.17 from the DAG repository on RHEL AS 4u5
with kernel 2.6.9-55.ELsmp

 
Received on Thu Jan 31 2008 - 13:05:41 CET