On Fri, 10 Feb 2017, Jens-U. Mozdzen wrote:

Hello *,

Zitat von Kai Krakow [off-list ref]:

quoted

[...]
The hardware block size (aka sector size) is not what is meant here...
You should use the biggest value. 8x512b fits into 4k. So bcache would
simply use 4k as the block size and it just works despite the sectors
being 512b.

sorry for using confusing terms - yes, I was talking about sector sizes.

quoted

What I meant is "make-bcacke --block X". It defaults to X=512b. I think
you may want to force it to 4k and see if your problem persists.

I checked my various bcache backing stores and cache devices and got pretty
inconsistent values. Time to clean up.

So trying to straighten things out, I started with a fresh backing device and
feel like something's broken here:

- created a new RAID device, which has a sector size of 4096 per underlying
disks:

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:~ # ll /sys/fs/bcache/
total 0
drwxr-xr-x 7 root root    0 Feb 10 11:37 32c8c1f9-268c-4405-8fd7-ab9f5acbe3fb
--w------- 1 root root 4096 Feb 10 11:35 register
--w------- 1 root root 4096 Feb 10 11:35 register_quiet
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.


--
Eric Wheeler

"myserver" has a running bcache setup in parallel, with the cache device
having a sector size of 512b (and bcache_super_show reports one sector per
block). Does this influence "make-bcache", although no cache is attached (and
the reported cset.uuid is different from the running bcache)?

Regards,
Jens



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