Date: Thu, 27 Mar 2014 10:02:11 +0100 From: "Ronald Klop" <ronald-lists@klop.ws> To: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org>, "Joar Jegleim" <joar.jegleim@gmail.com> Subject: Re: zfs l2arc warmup Message-ID: <op.xddh1xf3kndu52@ronaldradial.radialsg.local> In-Reply-To: <CAFfb-hpi20062%2BHCrSVhey1hVk9TAcOZAWgHSAP93RSov3sx4A@mail.gmail.com> References: <CAFfb-hpi20062%2BHCrSVhey1hVk9TAcOZAWgHSAP93RSov3sx4A@mail.gmail.com>
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On Thu, 27 Mar 2014 08:50:06 +0100, Joar Jegleim <joar.jegleim@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 > :) 2TB of l2arc? Why don't you put your data on SSD's, get rid of the l2arc and buy some extra RAM instead. Than you don't need any warm-up. For future questions, please provide more details about your setup. What are disks, what ssds, how much RAM. How is your pool configured? Mirror, raidz, ... Things like that. Ronald.
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