From owner-freebsd-questions@FreeBSD.ORG Fri May 16 16:35:39 2014 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 4AEF4CB2 for ; Fri, 16 May 2014 16:35:39 +0000 (UTC) Received: from mail.magehandbook.com (173-8-4-45-WashingtonDC.hfc.comcastbusiness.net [173.8.4.45]) by mx1.freebsd.org (Postfix) with ESMTP id 1DE402175 for ; Fri, 16 May 2014 16:35:38 +0000 (UTC) Received: from [192.168.1.50] (Mac-Pro.magehandbook.com [192.168.1.50]) by mail.magehandbook.com (Postfix) with ESMTP id 3gVZx00JRbz145; Fri, 16 May 2014 12:35:32 -0400 (EDT) Date: Fri, 16 May 2014 12:35:31 -0400 From: Daniel Staal To: David.I.Noel@gmail.com, FreeBSD Questions Subject: Re: Swap on ZFS Message-ID: <70EDDE5325B0B8DF55F19086@[192.168.1.50]> In-Reply-To: References: <53697D8B.2060906@gmail.com> <5369B4A1.40506@gmail.com> <5369B8A3.7020403@my.hennepintech.edu> <5369C376.7000307@gmail.com> <5369C434.1090409@my.hennepintech.edu> X-Mailer: Mulberry/4.0.8 (Mac OS X) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 May 2014 16:35:39 -0000 --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. ---------------------------------------------------------------