From owner-freebsd-fs@FreeBSD.ORG Thu May 12 08:42:49 2011 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 324A8106564A for ; Thu, 12 May 2011 08:42:49 +0000 (UTC) (envelope-from kraduk@gmail.com) Received: from mail-wy0-f182.google.com (mail-wy0-f182.google.com [74.125.82.182]) by mx1.freebsd.org (Postfix) with ESMTP id AC9788FC1B for ; Thu, 12 May 2011 08:42:47 +0000 (UTC) Received: by wyf23 with SMTP id 23so1318541wyf.13 for ; Thu, 12 May 2011 01:42:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=5l4bzEdxUZ/R8DtBDQb0sLziqCdB/UrDGDhJdcjONQ4=; b=jdlFa59LRxFvnKHrhqlB7C3ttX6u9ULrPKVNYz3Yqm+KSrAzN2NSqyNJ4AodndsC0e qD1kc3bIBTxZ1ufifWMwAayEJYiodRJq1NoYBdGULbKgo0A6jcAj5eBtv93JhmQkwWl5 HXYym3vZ4SVYr/jcGydUD5mzNtIoV6zJ9cZ/E= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=TANSlEFNsR6pPYmSfIi/dV/NStks5KlNMaOxE32iG7yQEp+HtniZQjf/6e2w+Byj2q SClNtxWGaiU/G9aDtdyJywTmsSuLXCODRvuFd1JaC2secG/Zpz5TS3+pulQRINbHrTPM LZMJ2N7FitD8/oLd1xpXbigv4huTFTLUWPE9Y= MIME-Version: 1.0 Received: by 10.216.63.130 with SMTP id a2mr1398863wed.61.1305189765647; Thu, 12 May 2011 01:42:45 -0700 (PDT) Received: by 10.216.93.70 with HTTP; Thu, 12 May 2011 01:42:45 -0700 (PDT) In-Reply-To: <20110511223849.GA65193@DataIX.net> References: <4DCA5620.1030203@dannysplace.net> <20110511100655.GA35129@icarus.home.lan> <4DCA66CF.7070608@digsys.bg> <20110511105117.GA36571@icarus.home.lan> <4DCA7056.20200@digsys.bg> <20110511120830.GA37515@icarus.home.lan> <20110511223849.GA65193@DataIX.net> Date: Thu, 12 May 2011 09:42:45 +0100 Message-ID: From: krad To: Jason Hellenthal Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-fs@freebsd.org Subject: Re: ZFS: How to enable cache and logs. X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 12 May 2011 08:42:49 -0000 On 11 May 2011 23:38, Jason Hellenthal wrote: > > Jeremy, > > On Wed, May 11, 2011 at 05:08:30AM -0700, Jeremy Chadwick wrote: > > On Wed, May 11, 2011 at 02:17:42PM +0300, Daniel Kalchev wrote: > > > On 11.05.11 13:51, Jeremy Chadwick wrote: > > > >Furthermore, TRIM support doesn't exist with ZFS on FreeBSD, so folk= s > > > >should also keep that in mind when putting an SSD into use in this > > > >fashion. > > > > > > By the way, what would be the use of TRIM for SLOG and L2ARC devices? > > > I see absolutely no benefit from TRIM for the L2ARC, because it is > > > written slowly (on purpose). Any current, or 1-2 generations back SS= D > > > would handle that write load without TRIM and without any performance > > > degradation. > > > > > > Perhaps TRIM helps with the SLOG. But then, it is wise to use SLC > > > SSD for the SLOG, for many reasons. The write regions on the SLC > > > NAND should be smaller (my wild guess, current practice may differ) > > > and the need for rewriting will be small. If you don't need to > > > rewrite already written data, TRIM does not help. Also, as far as I > > > understand, most "serious" SSDs (typical for SLC I guess) would have > > > twice or more the advertised size and always write to fresh cells, > > > scheduling an background erase of the 'overwritten' cell. > > > > AFAIK, drive manufacturers do not disclose just how much reallocation > > space they keep available on an SSD. I'd rather not speculate as to ho= w > > much, as I'm certain it varies per vendor. > > > > Lets not forget here: The size of the separate log device may be quite > small. A rule of thumb is that you should size the separate log to be abl= e > to handle 10 seconds of your expected synchronous write workload. It woul= d > be rare to need more than 100 MB in a separate log device, but the > separate log must be at least 64 MB. > > http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide > > > So in other words how much is TRIM really even effective give the above ? > > Even with a high database write load on the disks at full compacity of th= e > incoming link I would find it hard to believe that anyone could get the > ZIL to even come close to 512MB. > > > Given most SSD's come at a size greater than 32GB I hope this comes as a > early reminder that the ZIL you are buying that disk for is only going to > be using a small percent of that disk and I hope you justify cost over it= s > actual use. If you do happen to justify creating a ZIL for your pool then > I hope that you partition it wisely to make use of the rest of the space > that is untouched. > > For all other cases I would reccomend if you still want to have a ZIL tha= t > you take some sort of PCI->SD CARD or USB stick into account with > mirroring. > > -- > > Regards, (jhell) > Jason Hellenthal > > > You have just spotted a gap in the market I suspect. Maybe SSD manufacturers need to produce a sata based ssd of 1 or 2 gb of the fastest write speed available flash on the market. Produce it for < =A350 and you should have a big market