* Read cache contents cleared on boot?
@ 2013-11-06 22:08 Larkin Lowrey
2013-12-08 18:32 ` Rolf Fokkens
0 siblings, 1 reply; 3+ messages in thread
From: Larkin Lowrey @ 2013-11-06 22:08 UTC (permalink / raw)
To: linux-bcache-u79uwXL29TY76Z2rM5mHXA
When I boot my cache usage returns to 1.3GB even when it was nearly full
at shutdown (as reported by bcache-status). Are the read cache contents
not retained across a reboot?
I'm running fedora 19 w/ kernel-3.11.6-201.fc19.x86_64 and bcache-tools
built from git yesterday afternoon.
The machine in question is a backup server that boots nightly (via WOL)
runs all backup jobs then shuts down. The backup process spends most of
its time seeking (probably inodes) and I was hoping that the cache would
be warm on boot so those random reads would come from cache.
The cache device is a 48GB LVM LV on top of a 2 disk raid1 (60GB SSDs).
The backing devices are two 16 drive md raid6 arrays which act as LVM PVs.
Backup run time has not improved which supports the idea that the read
cache is empty on boot.
--Larkin
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Read cache contents cleared on boot?
2013-11-06 22:08 Read cache contents cleared on boot? Larkin Lowrey
@ 2013-12-08 18:32 ` Rolf Fokkens
2013-12-10 23:25 ` Larkin Lowrey
0 siblings, 1 reply; 3+ messages in thread
From: Rolf Fokkens @ 2013-12-08 18:32 UTC (permalink / raw)
To: Larkin Lowrey, linux-bcache
On 11/06/2013 11:08 PM, Larkin Lowrey wrote:
> When I boot my cache usage returns to 1.3GB even when it was nearly full
> at shutdown (as reported by bcache-status). Are the read cache contents
> not retained across a reboot?
Same here: After running for a while bcache-status reports a Total Cache
Used of 2.1GB. After reboot it's back to 910MB all the time. Did you get
an explanation for this?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Read cache contents cleared on boot?
2013-12-08 18:32 ` Rolf Fokkens
@ 2013-12-10 23:25 ` Larkin Lowrey
0 siblings, 0 replies; 3+ messages in thread
From: Larkin Lowrey @ 2013-12-10 23:25 UTC (permalink / raw)
To: Rolf Fokkens, linux-bcache
On 12/8/2013 12:32 PM, Rolf Fokkens wrote:
> On 11/06/2013 11:08 PM, Larkin Lowrey wrote:
>> When I boot my cache usage returns to 1.3GB even when it was nearly full
>> at shutdown (as reported by bcache-status). Are the read cache contents
>> not retained across a reboot?
> Same here: After running for a while bcache-status reports a Total
> Cache Used of 2.1GB. After reboot it's back to 910MB all the time. Did
> you get an explanation for this?
I never got an explanation but I have a theory. My cache has started
booting with much more total cache used reported. My theory is that
garbage collection is occurring on boot and that my pre-shutdown numbers
contain a lot of dirty pages. I plan to verify this, when I get a
chance, by forcing a garbage collection before shutdown and comparing
the post GC numbers to the post boot numbers.
--Larkin
^ permalink raw reply [flat|nested] 3+ messages in thread
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2013-11-06 22:08 Read cache contents cleared on boot? Larkin Lowrey
2013-12-08 18:32 ` Rolf Fokkens
2013-12-10 23:25 ` Larkin Lowrey
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