Hi
I was in the process of testing linux-bcache but was seeing some strange
behaviour so I thought I would remount my cached filesystem. I then
noticed that the performance results started looking like the cache just
wasn't there, so I unregistered it:
bcache: Cache set be008612-38aa-4082-9f42-1bada25cb002 unregistered
bcache: Caching disabled for sdc
but now when I try to register it again, I get bcache: error
opening /dev/sdb: device busy.
I haven't tried rebooting yet but probably will do after I've sent this
message.
These were the strange results I was getting that prompted me to unmount
and remount the filesystems.
Setup: hardware RAID 5 16 disk array with 2 partitions, 1 Intel 40GB SSD
for bcache.
Filesystem Size Used Avail Use% Mounted on
/dev/bcache0 1.9T 26G 1.8T 2% /data33
/dev/sdd 1.9T 23G 1.8T 2% /data34
Wrote an 8GB file to each filesystem, then tried reading it back.
Machine has 8GB RAM.
Speed for random reads from identical SSD = 181.766523 MB/Sec, random
read test done in the following order with measured speed in MB/Sec. The
random IO is actually just reading with a 4GB stride, wrapping around at
the end of the file.
/data33 49
/data34 114
/data33 114
/data33 and /data44 simultaneously 78 and 59 respectively
/data33 76
/data33 68
/data34 114
/data34 96
/data34 69
/data34 74
/data33 118
/data33 40
/data34 91
After remounting both filesystems:
/data34 148
/data33 120
/data34 120
/data33 82
After unregistering the cache
/data33 65
/data34 83
/data33 99
/data34 113
Cheers,
Franco
Not sure what's going on with not being able to register again - not a
lot of info to go off of. It was working last I checked in the
bcache-3.2-dev branch, it might be buggy in the older bcache branch.
From your numbers it looks like the 8 gb of data wasn't in the cache -
bcache bypasses sequential IO by default. You can flip it off by
echoing 0 to sequential_cutoff.
On Tue, Feb 14, 2012 at 9:26 PM, Franco [off-list ref] wrote:
Hi
I was in the process of testing linux-bcache but was seeing some strange
behaviour so I thought I would remount my cached filesystem. I then
noticed that the performance results started looking like the cache just
wasn't there, so I unregistered it:
bcache: Cache set be008612-38aa-4082-9f42-1bada25cb002 unregistered
bcache: Caching disabled for sdc
but now when I try to register it again, I get bcache: error
opening /dev/sdb: device busy.
I haven't tried rebooting yet but probably will do after I've sent this
message.
These were the strange results I was getting that prompted me to unmount
and remount the filesystems.
Setup: hardware RAID 5 16 disk array with 2 partitions, 1 Intel 40GB SSD
for bcache.
Filesystem Size Used Avail Use% Mounted on
/dev/bcache0 1.9T 26G 1.8T 2% /data33
/dev/sdd 1.9T 23G 1.8T 2% /data34
Wrote an 8GB file to each filesystem, then tried reading it back.
Machine has 8GB RAM.
Speed for random reads from identical SSD = 181.766523 MB/Sec, random
read test done in the following order with measured speed in MB/Sec. The
random IO is actually just reading with a 4GB stride, wrapping around at
the end of the file.
/data33 49
/data34 114
/data33 114
/data33 and /data44 simultaneously 78 and 59 respectively
/data33 76
/data33 68
/data34 114
/data34 96
/data34 69
/data34 74
/data33 118
/data33 40
/data34 91
After remounting both filesystems:
/data34 148
/data33 120
/data34 120
/data33 82
After unregistering the cache
/data33 65
/data34 83
/data33 99
/data34 113
Cheers,
Franco
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