Hi All
I'm doing some testing with OpenSUSE Leap 42.1, it ships with kernel 4.1.12 but I've also tested with 4.1.24
When I map an image with the kernel RBD client, max_sectors_kb = 127. I'm unable to increase:
# echo 4096 > /sys/block/rbd0/queue/max_sectors_kb
-bash: echo: write error: Invalid argument
I'm seeing very poor sequential read performance which I suspect is a result of max_sectors_kb being stuck at 127
Does anyone know what's going on here?
The behavior I've seen on older kernels is max_sectors_kb is set to 512 but can be increased up to max_hw_sectors_kb. On newer kernels max_sectors_kb matches the image's object size.
The image is default 4MB object size, here's everything in /sys/block/rbd0/queue:
# grep -r .
nomerges:0
logical_block_size:512
rq_affinity:1
discard_zeroes_data:1
max_segments:128
max_segment_size:4194304
rotational:0
scheduler:none
read_ahead_kb:512
max_hw_sectors_kb:4096
discard_granularity:4194304
discard_max_bytes:4194304
write_same_max_bytes:0
max_integrity_segments:0
max_sectors_kb:127
physical_block_size:512
add_random:0
nr_requests:128
minimum_io_size:4194304
hw_sector_size:512
optimal_io_size:4194304
iostats:1
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