Hi,
I'm currently running the latest bcache (non-dev) on an ubuntu 12.04,
and it seems to me that bcache doesn't cache anything
The setup is as follow:
- One drive for the system
- a 480 GB SSD caching device (/dev/sdb)
- a 10 drives Raid 5 (on a HP P410 controller) backing device
(/dev/sdc)
- 36 GB ram
/dev/bcache0 mounted as /home
The server is a file server, with lots of file but few of them served
frequently. So that's why I've put bcache on it, to have frequently
asked files on the caching device (which are bigger than the server's
ram)
I've filled the server with 16 TB of datas, and I see little to no
usage of /dev/sdb
# iostat -x 30
avg-cpu: %user %nice %system %iowait %steal %idle
0.05 0.00 0.74 10.92 0.00 88.30
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s
avgrq-sz avgqu-sz await r_await w_await svctm %util
sda 0.00 0.40 0.00 0.83 0.00 5.07
12.16 0.00 0.00 0.00 0.00 0.00 0.00
sdb 0.27 0.03 1.10 0.17 136.57 0.37
216.21 0.00 0.95 1.09 0.00 0.53 0.07
sdc 0.00 0.00 185.53 0.03 23750.93 0.03
255.98 3.14 16.90 16.90 0.00 4.40 81.59
bcache0 0.00 0.00 186.67 0.10 23896.00 0.32
255.89 0.00 16.81 16.82 0.00 0.00 0.00
sequential_cutoff and sequential_merge are echoed 0 to disable them,
because I want sequential IOs to be cached
I get strange numbers from the variables. Some seems to indicate that
bcache is doing its work, others seems not.
I'm totally puzzled. Am I doing something wrong ? It bcache suited for
what I want to do ? Is it a bug ?
I've even tried to recreate the caching device to get rid of the data
that was on it during data was put on the backing device.
As noted in this mailing-list, I made some writes to the device to
allow the btree to split/grow if needed, and seen no changes.
Here are the details :
# cat /sys/block/bcache0/bcache/cache/internal/active_journal_entries
3
# cat /sys/block/bcache0/bcache/cache/internal/bset_tree_stats
btree nodes: 1
written sets: 2
unwritten sets: 1
written key bytes: 156768
unwritten key bytes: 96
floats: 1222
failed: 63
# cat /sys/block/bcache0/bcache/cache/internal/btree_nodes
1
# cat /sys/block/bcache0/bcache/cache/internal/btree_used_percent
46
# cat /sys/block/bcache0/bcache/cache/average_key_size
384k
# cat /sys/block/bcache0/bcache/cache/btree_cache_size
0
# cat /sys/block/bcache0/bcache/cache/cache_available_percent
99
# cat /sys/block/bcache0/bcache/cache/root_usage_percent
47
# cat /sys/block/bcache0/bcache/cache/tree_depth
0
# cat /sys/block/bcache0/bcache/cache_mode
writethrough [writeback] writearound none
# cat /sys/block/bcache0/bcache/readahead
1.0M
# cat /sys/block/bcache0/bcache/stats_hour/bypassed
0
# cat /sys/block/bcache0/bcache/stats_hour/cache_hit_ratio
100
# cat /sys/block/bcache0/bcache/stats_hour/cache_hits
960779
# cat /sys/block/bcache0/bcache/stats_hour/cache_misses
0
# cat /sys/block/bcache0/bcache/stats_hour/cache_readaheads
0
# cat /sys/block/bcache0/bcache/cache/cache0/freelist_percent
0
# cat /sys/block/bcache0/bcache/cache/cache0/priority_stats
Unused: 89%
Metadata: 0%
Average: 4141
Sectors per Q: 3109760
Quantiles: [4162 4189 4193 4197 4201 4205 4209 4213 4217 4221 4225
4229 4233 4237 4241 4245 4249 4253 4257 4260 4264 4268 4272 4276 4280
4284 4288 4292 4296 4300 4304]
# cat /sys/block/bcache0/bcache/cache/cache0/written
47.4G
# cat /sys/block/bcache0/bcache/cache/cache0/cache_replacement_policy
[lru] fifo random
# cat /sys/block/bcache0/bcache/cache/cache0/nbuckets
915661
# cat /sys/block/bcache0/bcache/cache/cache0/metadata_written
13.3M
I don't know what to try. At first I used bcache-3.2, and seeing this
beavior made me switch to bcache and 3.8 kernel. Tried bcache-dev, too,
but the server doesn't boot, kernel stuck in a softlock @[bcache:345]
(no idea of the meaning)
What am I doing wrong ?
There's little to no activity on the caching device, I though there
would be write operations to cache served files, but the only writes are
when I put new files. The pattern is 99% read of big files (~ from 100
MB to 10 GB)
Thank you
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