Re: Ceph cache tier, flushed objects does not appear to be written on disk

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On Thursday, April 21, 2016, Benoît LORIOT <benoit.loriot@xxxxxxxx> wrote:
Hello,

we want to disable readproxy cache tier but before doing so we would like to make sure we won't loose data.

Is there a way to confirm that flush actually write objects to disk ?

We're using ceph version 0.94.6.


I tried that, with cephfs_data_ro_cache being the hot storage pool and cephfs_data being the cold storage pool

# rados -p cephfs_data_ro_cache ls

then choose a random object in the list : 100004d6142.00000000

Find the object on cache disk :

# ceph osd map cephfs_data_ro_cache 100004d6142.00000000
osdmap e301 pool 'cephfs_data_ro_cache' (6) object '100004d6142.00000000' -> pg 6.d010000 (6.0) -> up ([4,5,8], p4) acting ([4,5,8], p4)

Object is in the pg 6.0 on OSD 4, 5 and 8, I can find the file on disk.

# ls -l /var/lib/ceph/osd/ceph-4/current/6.0_head/DIR_0/DIR_0/DIR_0/DIR_0/100004d6142.00000000__head_0D010000__6
-rw-r--r--. 1 root root 0 Apr  8 19:36 /var/lib/ceph/osd/ceph-4/current/6.0_head/DIR_0/DIR_0/DIR_0/DIR_0/100004d6142.00000000__head_0D010000__6

Flush the object :

# rados -p cephfs_data_ro_cache cache-try-flush 100004d6142.00000000

Find the object on disk :

# ceph osd map cephfs_data 100004d6142.00000000
osdmap e301 pool 'cephfs_data' (1) object '100004d6142.00000000' -> pg 1.d010000 (1.0) -> up ([1,7,2], p1) acting ([1,7,2], p1)

Object is in the pg 1.0 on OSD 1, 7 and 2, I can't find the file on disk on any of the 3 OSDs

# ls -l /var/lib/ceph/osd/ceph-1/current/1.0_head/DIR_0/DIR_0/DIR_0/DIR_0/100004d6142.*
ls: cannot access /var/lib/ceph/osd/ceph-1/current/1.0_head/DIR_0/DIR_0/DIR_0/DIR_0/100004d6142.*: No such file or directory



What am I doing wrong ? To me it seems that nothing is actually flushed to disk.


Is the directory actually hashed four levels deep? Or is it shallower and you're looking too far down?
-Greg
 
Thank you,
Ben.
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