Date: Fri, 16 May 2014 12:35:31 -0400 From: Daniel Staal <DStaal@usa.net> To: David.I.Noel@gmail.com, FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: Swap on ZFS Message-ID: <70EDDE5325B0B8DF55F19086@[192.168.1.50]> In-Reply-To: <CAHAXwYBoAda0cA6EdAQNjzUS2RHxAUdWm9qKJ-GbWgDF9c79xQ@mail.gmail.com> References: <CAHAXwYA9NBsYTpUGCZ_5f%2B_qDuvS%2BbN9vE4GAZhpRhWVWCwi7g@mail.gmail.com> <53697D8B.2060906@gmail.com> <C1DCD8EEE8523B91197B6D82@192.168.1.50> <5369B4A1.40506@gmail.com> <5369B8A3.7020403@my.hennepintech.edu> <5369C376.7000307@gmail.com> <5369C434.1090409@my.hennepintech.edu> <CALfReyffOD0H9Xu2Exkk56SLA8hWnQNeYWsiRiQ5D2zvu=ar1g@mail.gmail.com> <CAHAXwYBoAda0cA6EdAQNjzUS2RHxAUdWm9qKJ-GbWgDF9c79xQ@mail.gmail.com>
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--As of May 12, 2014 7:01:17 AM -0500, David Noel is alleged to have said: > However, I don't see any way around the rumored issue of the system > hanging every time all my RAM is in use and I need to hit swap. Is > this still the default behavior? The wiki says yes. I suppose I could > test it myself fairly easily. But what would the solution be? If I > test it and it hangs I'd like to be able to suggest a solution in the > PR. Would adding a tunable that allowed me to reserve x MB for ZFS be > the solution? Out of curiousity, what would that value need to be set > to? How much memory does ZFS need available to write to disk? --As for the rest, it is mine. Having hit it a couple of times, I'd say it's a bit more complicated than that description, but yeah, that's still the behavior from my experience. Failure can be more complicated than 'hang' though, and triggering it can be a bit hit-or-miss. A tunable like that sounds like a good solution. I'm not sure what the value would need to be set at though. I'm not even sure if it's a constant or dependent on blocksize and other factors. I'm pretty sure the memory needed per block is a defined amount someplace, but ZFS likes to group IO where possible, so a 'safe' amount might vary by the amount of writes it can have queued at any particular moment. (Which is a tunable.) Daniel T. Staal --------------------------------------------------------------- This email copyright the author. Unless otherwise noted, you are expressly allowed to retransmit, quote, or otherwise use the contents for non-commercial purposes. This copyright will expire 5 years after the author's death, or in 30 years, whichever is longer, unless such a period is in excess of local copyright law. ---------------------------------------------------------------
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