Date: Mon, 8 Feb 2010 17:17:35 +0100 From: Guido Falsi <mad@madpilot.net> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: freebsd-stable@freebsd.org Subject: Re: ATA_CAM + ZFS gives short 1-2 seconds system freeze on disk load Message-ID: <20100208161735.GB43063@megatron.madpilot.net> In-Reply-To: <20100208145147.GA3733@icarus.home.lan> References: <20100208143329.GA12057@megatron.madpilot.net> <20100208145147.GA3733@icarus.home.lan>
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On Mon, Feb 08, 2010 at 06:51:47AM -0800, Jeremy Chadwick wrote: > On Mon, Feb 08, 2010 at 03:33:29PM +0100, Guido Falsi wrote: > > > > It gets very annoying and I don't remember this happening before > > activating the ATA_CAM flag. There was some slowdown with big disk > > access, but not a total freeze. > > This happens without ATA_CAM (e.g. using ataahci(4) or any other > controller driver). > > The behaviour you're describing (bursty heavy disk I/O that stalls the > subsystem) is pretty much the norm on all FreeBSD systems I've seen with > ZFS. When it starts happening, it's easy to notice/follow using "zpool > iostat 1" or "gstat -I500ms". Lots of I/O will happen (read or write) > and the ARC is essentially being thrashed -- said utilities won't show > any I/O counters incrementing until some threshold is reached, where > you'll see a massive amount of I/O reported, during which time the > system is sluggish (beyond acceptable levels, IMHO). A few seconds > later, the I/O counters start reporting 0 as the ARC gets used, then > a few seconds massive I/O, rinse lather repeat. > > I've seen Solaris 10 systems which behave the same way, and others which > don't. I don't know what causes things to start behaving this way. Thank you for the explanation. I in fact see the same problem with the legacy ata driver. I see this is something not trivial to fix, so I don't want to put too much burden on the pople who brought us zfs, which is anyway a great thing! Anyway the sluggish responsiveness of the system during these bursts is a problem for desktop use. I see that ZFS is mainly a server oriented FS, but this should be addressed sometime in the future I think. > > > BTW there's another thing that shows up on this machine. Lately, this > > too after putting the option ATA_CAM in the kernel, during boot there is > > a long pause(exactly one minute, as the message below states) in this > > point of the dmesg: > > This should probably be discussed in a different thread. I'll follow your suggestion and post a new thread about this. Thank you again! -- Guido Falsi <mad@madpilot.net>
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