flashcache with mdadm and LVM
- by Backtogeek
I am having trouble setting up flashcache on a system with LVM and mdadm, I suspect I am either just missing an obvious step or getting some mapping wrong and hoped someone could point me in the right direction?
system info:
CentOS 6.4 64 bit
mdadm config
md0 : active raid1 sdd3[2] sde3[3] sdf3[4] sdg3[5] sdh3[1] sda3[0]
204736 blocks super 1.0 [6/6] [UUUUUU]
md2 : active raid6 sdd5[2] sde5[3] sdf5[4] sdg5[5] sdh5[1] sda5[0]
3794905088 blocks super 1.1 level 6, 512k chunk, algorithm 2 [6/6] [UUUUUU]
md3 : active raid0 sdc1[1] sdb1[0]
250065920 blocks super 1.1 512k chunks
md1 : active raid10 sdh1[1] sda1[0] sdd1[2] sdf1[4] sdg1[5] sde1[3]
76749312 blocks super 1.1 512K chunks 2 near-copies [6/6] [UUUUUU]
pcsvan
PV /dev/mapper/ssdcache VG Xenvol lvm2 [3.53 TiB / 3.53 TiB free]
Total: 1 [3.53 TiB] / in use: 1 [3.53 TiB] / in no VG: 0 [0 ]
flashcache create command used:
flashcache_create -p back ssdcache /dev/md3 /dev/md2
pvdisplay
--- Physical volume ---
PV Name /dev/mapper/ssdcache
VG Name Xenvol
PV Size 3.53 TiB / not usable 106.00 MiB
Allocatable yes
PE Size 128.00 MiB
Total PE 28952
Free PE 28912
Allocated PE 40
PV UUID w0ENVR-EjvO-gAZ8-TQA1-5wYu-ISOk-pJv7LV
vgdisplay
--- Volume group ---
VG Name Xenvol
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 2
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 1
Act PV 1
VG Size 3.53 TiB
PE Size 128.00 MiB
Total PE 28952
Alloc PE / Size 40 / 5.00 GiB
Free PE / Size 28912 / 3.53 TiB
VG UUID 7vfKWh-ENPb-P8dV-jVlb-kP0o-1dDd-N8zzYj
So that is where I am at, I thought that was the job done however when creating a logical volume called test and mounting it is /mnt/test the sequential write is pathetic, 60 ish MB/s
/dev/md3 has 2 x SSD's in Raid0 which alone is performing at around 800 MB/s sequential write and I am trying to cache /dev/md2 which is 6 x 1TB drives in raid6
I have read a number of pages through the day and some of them here, it is obvious from the results that the cache is not functioning but I am unsure why.
I have added the filter line in the lvm.conf
filter = [ "r|/dev/sdb|", "r|/dev/sdc|", "r|/dev/md3|" ]
It is probably something silly but the cache is clearly performing no writes so I suspect I am not mapping it or have not mounted the cache correctly.
dmsetup status
ssdcache: 0 7589810176 flashcache stats:
reads(142), writes(0)
read hits(133), read hit percent(93)
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)
force_clean_block(0)
disk reads(9), disk writes(0) ssd reads(133) ssd writes(9)
uncached reads(0), uncached writes(0), uncached IO requeue(0)
disk read errors(0), disk write errors(0) ssd read errors(0) ssd write errors(0)
uncached sequential reads(0), uncached sequential writes(0)
pid_adds(0), pid_dels(0), pid_drops(0) pid_expiry(0)
lru hot blocks(31136000), lru warm blocks(31136000)
lru promotions(0), lru demotions(0)
Xenvol-test: 0 10485760 linear
I have included as much info as I can think of, look forward to any replies.
