From owner-freebsd-fs@FreeBSD.ORG Wed Oct 12 12:03:04 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 A229D106566C for ; Wed, 12 Oct 2011 12:03:04 +0000 (UTC) (envelope-from freebsd-fs@m.gmane.org) Received: from lo.gmane.org (lo.gmane.org [80.91.229.12]) by mx1.freebsd.org (Postfix) with ESMTP id 5E6FF8FC25 for ; Wed, 12 Oct 2011 12:03:04 +0000 (UTC) Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1RDxWX-0005VN-0S for freebsd-fs@freebsd.org; Wed, 12 Oct 2011 14:03:01 +0200 Received: from dyn1206-83.wlan.ic.ac.uk ([129.31.206.83]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 12 Oct 2011 14:03:00 +0200 Received: from jtotz by dyn1206-83.wlan.ic.ac.uk with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 12 Oct 2011 14:03:00 +0200 X-Injected-Via-Gmane: http://gmane.org/ To: freebsd-fs@freebsd.org From: Johannes Totz Date: Wed, 12 Oct 2011 13:02:47 +0100 Lines: 31 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: dyn1206-83.wlan.ic.ac.uk User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:7.0.1) Gecko/20110929 Thunderbird/7.0.1 In-Reply-To: Subject: Re: ZFS/compression/performance 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: Wed, 12 Oct 2011 12:03:04 -0000 On 12/10/2011 00:25, Dennis Glatting wrote: > I would appreciate someone knowledgeable in ZFS point me in the right > direction. > > I have several ZFS arrays, some using gzip for compression. The > compressed arrays hold very large text documents (10MB->20TB) and are > highly compressible. Reading the files from a compressed data sets is > fast with little load. However, writing to the compressed data sets > incurs substantial load on the order of a load average from 12 to 20. > > My questions are: > > 1) Why such a heavy load on writing? > 2) What kind of limiters can I put into effect to reduce load > without impacting compressibilty? For example, is there some > variable to controls the number of parallel compression > operations? > > I have a number of different systems. Memory is 24GB on each of the two > large data systems, SSD (Revo) for cache, and a SATA II ZIL. One system > is a 6 core i7 @ 3.33 GHz and the other 4 core ii7 @ 2.93 GHz. The > arrays are RAIDz using cheap 2TB disks. Artem gave you a pretty good explanation. I just did a simple write test yesterday: 1) 6 MB/sec for gzip, 1.36x ratio 2) 34 MB/sec for lzjb, 1.23x ratio I'll stick with lzjb. It's good enough to get rid of most of the redundancy and speed is acceptable.