Date: Mon, 12 May 2014 07:01:17 -0500 From: David Noel <david.i.noel@gmail.com> To: krad <kraduk@gmail.com> Cc: Andrew Berg <aberg010@my.hennepintech.edu>, FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: Swap on ZFS Message-ID: <CAHAXwYBoAda0cA6EdAQNjzUS2RHxAUdWm9qKJ-GbWgDF9c79xQ@mail.gmail.com> In-Reply-To: <CALfReyffOD0H9Xu2Exkk56SLA8hWnQNeYWsiRiQ5D2zvu=ar1g@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>
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> the check summing of swap is quite a big deal in my opinion. You have your > nice big server with ECC ram, but you do need to page some stuff in and > out. Now you go and get some corruption on your disks, which you then feed > back into your ram making the ecc irrelevant. Now that, I think, is a very interesting point, and one I hadn't considered. I see a great deal of value in having checksumming enabled on a swap volume/partition. What is the default behavior when I create a freebsd-swap partition with gpart, then hand it to the OS with swapon? Is there any sort of error correction mechanism in place? That alone would make a very strong case for swap on ZFS. 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?
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