zfs l2arc warmup

[Joar Jegleim]

thnx, I found some similar post over at illumos related to persistent
l2arc yesterday. It's interesting :)

But it's really not a problem for me how long it takes to warm up the
l2arc, if it takes a week that's ok. After all I don't plan on
reboot'ing this setup very often + I have 2 servers so I have the
option to let the server warmup until i hook it into production again
after maintenance / patch upgrade and so on .

I'm just curious about wether or not the l2arc warmup itself, or if I
would have to do that manual rsync to force l2arc warmup.

On 27 March 2014 10:16, krad <kraduk at gmail.com> wrote:
> not sure if its made it into freebsd yet but
>
> https://www.illumos.org/issues/3525
>
>
>
>
> On 27 March 2014 07:50, Joar Jegleim <joar.jegleim at gmail.com> wrote:
>>
>> Hi list !
>>
>> I struggling to get a clear understanding of how the l2arc get warm (
>> zfs).
>> It's a FreeBSD 9.2-RELEASE server.
>>
>> From various forum I've come up with this which I have in my
>> /boot/loader.conf
>> # L2ARC tuning
>> # Maximum number of bytes written to l2arc per feed
>> # 8MB (actuall=vfs.zfs.l2arc_write_max*(1000 / vfs.zfs.l2arc_feed_min_ms))
>> # so 8MB every 200ms = 40MB/s
>> vfs.zfs.l2arc_write_max=8388608
>> # Mostly only relevant at the first few hours after boot
>> # write_boost, speed to fill l2arc until it is filled (after boot)
>> # 70MB, same rule applys, multiply by 5 = 350MB/s
>> vfs.zfs.l2arc_write_boost=73400320
>> # Not sure
>> vfs.zfs.l2arc_headroom=2
>> # l2arc feeding period
>> vfs.zfs.l2arc_feed_secs=1
>> # minimum l2arc feeding period
>> vfs.zfs.l2arc_feed_min_ms=200
>> # control whether streaming data is cached or not
>> vfs.zfs.l2arc_noprefetch=1
>> # control whether feed_min_ms is used or not
>> vfs.zfs.l2arc_feed_again=1
>> # no read and write at the same time
>> vfs.zfs.l2arc_norw=1
>>
>> But what I really wonder is how does the l2arc get warmed up ?
>> I'm thinking of 2 scenarios:
>>
>> a.: when arc is full, stuff that evict from arc is put over in l2arc,
>> that means that files in the fs that are never accessed will never end
>> up in l2arc, right ?
>>
>> b.: zfs run through fs in the background and fill up the l2arc for any
>> file, regardless if it has been accessed or not ( this is the
>> 'feature' I'd like )
>>
>> I suspect scenario a is what really happens, and if so, how does
>> people warmup the l2arc manually (?)
>> I figured that if I rsync everything from the pool I want to be
>> cache'ed, it will fill up the l2arc for me, which I'm doing right now.
>> But it takes 3-4 days to rsync the whole pool .
>>
>> Is this how 'you' do it to warmup the l2arc, or am I missing something ?
>>
>> The thing is with this particular pool is that it serves somewhere
>> between 20 -> 30 million jpegs for a website. The front page of the
>> site will for every reload present a mosaic of about 36 jpegs, and the
>> jpegs are completely randomly fetched from the pool.
>> I don't know what jpegs will be fetched at any given time, so I'm
>> installing about 2TB of l2arc ( the pool is about 1.6TB today) and I
>> want the whole pool to be available from the l2arc .
>>
>>
>> Any input on my 'rsync solution' to warmup the l2arc is much appreciated
>> :)
>>
>>
>> --
>> ----------------------
>> Joar Jegleim
>> Homepage: http://cosmicb.no
>> Linkedin: http://no.linkedin.com/in/joarjegleim
>> fb: http://www.facebook.com/joar.jegleim
>> AKA: CosmicB @Freenode
>>
>> ----------------------
>> _______________________________________________
>> freebsd-fs at freebsd.org mailing list
>> http://lists.freebsd.org/mailman/listinfo/freebsd-fs
>> To unsubscribe, send any mail to "freebsd-fs-unsubscribe at freebsd.org"
>
>



-- 
----------------------
Joar Jegleim
Homepage: http://cosmicb.no
Linkedin: http://no.linkedin.com/in/joarjegleim
fb: http://www.facebook.com/joar.jegleim
AKA: CosmicB @Freenode

----------------------