facebook/flashcache — Issue #36: Looks like flashcache no cache data
Author: easyjohn
Created: 2011-10-22 15:24:25+00:00
State: open

Create flashcache for device /dev/md0
"flashcache_create -v -p back ssd_cache /dev/sda2 /dev/md0"

Over /dev/md0 used lvm partitions, formatted ext4.
Started nfs server, fev clients write/read files.
No activity seen on ssh drive.
iostat show only hdd in md0 activity.

dmsetup stats not increased:

# dmsetup status ssd_cache
0 11720988672 flashcache stats:
reads(11), writes(0)
read hits(0), read hit percent(0)
write hits(0) write hit percent(0)
dirty write hits(0) dirty write hit percent(0)
replacement(0), write replacement(0)
write invalidates(0), read invalidates(0)
pending enqueues(0), pending inval(0)
metadata dirties(0), metadata cleans(0)
metadata batch(0) metadata ssd writes(0)
cleanings(0) fallow cleanings(0)
no room(0) front merge(0) back merge(0)
disk reads(11), disk writes(0) ssd reads(0) ssd writes(11)
uncached reads(0), uncached writes(0), uncached IO requeue(0)
pid_adds(0), pid_dels(0), pid_drops(0) pid_expiry(0)
# dmsetup table ssd_cache
ssd_cache: 0 11720988672 flashcache conf:
ssd dev (/dev/sda2), disk dev (/dev/md0) cache mode(WRITE_BACK)
capacity(40798M), associativity(512), data block size(4K) metadata block size(4096b)
total blocks(10444288), cached blocks(11), cache percent(0)
dirty blocks(0), dirty percent(0)
nr_queued(0)
Size Hist: 4096:22