Hi Eric,
Zitat von Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx>:
On Fri, 10 Feb 2017, Jens-U. Mozdzen wrote:
[...]
myserver:~ # blockdev --getss /dev/md125
4096
- created the bcache super block
myserver:~ # make-bcache -B --block 4096b /dev/md125
UUID: 05d4d36a-ef17-4ecb-99d4-0a0eeec03941
Set UUID: dd4165a9-47ca-4e35-9e7a-5968e1e40d92
version: 1
block_size: 8
data_offset: 16
myserver:~ # bcache-super-show /dev/md125
sb.magic ok
sb.first_sector 8 [match]
sb.csum F4E616E067FA3C45 [match]
sb.version 1 [backing device]
dev.label (empty)
dev.uuid 05d4d36a-ef17-4ecb-99d4-0a0eeec03941
dev.sectors_per_block 8
dev.sectors_per_bucket 1024
dev.data.first_sector 16
dev.data.cache_mode 0 [writethrough]
dev.data.cache_state 0 [detached]
cset.uuid dd4165a9-47ca-4e35-9e7a-5968e1e40d92
myserver:~ # [...]
Why does it report 8 sectors per block? With 4k per sector, that'd
be a block
size of 32k?
Its in 512b units and 8*512=4096. Lots of things are in units of 512 even
though your block size is 4096. Its correct, it just looks funny since
you have 4k sectors.
first of all, thank you for that information, I succeeded in setting
up that specific bcache scenario, have populated it and found no
problems so far.
Once I had a few spare minutes, I double-checked the source code of
make-bcache and bcache-show-super and indeed, there's hardcoded the
factor of 512 bytes. Nothing wrong with that, but I strongly suggest
to change both tools to include some unit information:
--- cut here ---
myserver:~ # make-bcache -B --block 4096b /dev/md125
[...]
block_size: 8 (units of 512 octets)
myserver:~ # bcache-super-show /dev/md125
[...]
dev.sectors_per_block 8 (pseudo-sectors of 512 octets each)
--- cut here ---
dev.sectors_per_block is especially misleading in its current display,
because that data element actually does *not* relate to native block
device sectors.
Both changes would be purely cosmetic and not altering current functionality.
It might be favorable (AKA "better readable") to instead output the
"block_size" in bytes/octets in both places, instead of just dumping
the value of the super block element.
Regards,
J
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