From owner-freebsd-fs@freebsd.org Wed Apr 27 03:24:45 2016 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 0670DB1DCFF for ; Wed, 27 Apr 2016 03:24:45 +0000 (UTC) (envelope-from paul@pk1048.com) Received: from cpanel61.fastdnsservers.com (server61.fastdnsservers.com [216.51.232.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id CA8821DBA for ; Wed, 27 Apr 2016 03:24:44 +0000 (UTC) (envelope-from paul@pk1048.com) Received: from pool-100-4-209-221.albyny.fios.verizon.net ([100.4.209.221]:64521 helo=[192.168.2.133]) by cpanel61.fastdnsservers.com with esmtpsa (TLSv1:ECDHE-RSA-AES256-SHA:256) (Exim 4.86_1) (envelope-from ) id 1avFIR-002r4P-7t; Tue, 26 Apr 2016 21:33:47 -0500 Subject: Re: How to speed up slow zpool scrub? Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Content-Type: text/plain; charset=utf-8 From: PK1048 In-Reply-To: <571FEB34.7040305@andyit.com.au> Date: Tue, 26 Apr 2016 22:33:44 -0400 Cc: freebsd-fs@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: <56C0A956-F134-4A8D-A8B6-B93DCA045BE4@pk1048.com> References: <698816653.2698619.1461685653634.JavaMail.yahoo.ref@mail.yahoo.com> <698816653.2698619.1461685653634.JavaMail.yahoo@mail.yahoo.com> <571F9897.2070008@quip.cz> <571FEB34.7040305@andyit.com.au> To: Andy Farkas X-Mailer: Apple Mail (2.3124) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cpanel61.fastdnsservers.com X-AntiAbuse: Original Domain - freebsd.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - pk1048.com X-Get-Message-Sender-Via: cpanel61.fastdnsservers.com: authenticated_id: info@pk1048.com X-Authenticated-Sender: cpanel61.fastdnsservers.com: info@pk1048.com X-Source: X-Source-Args: X-Source-Dir: X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Apr 2016 03:24:45 -0000 > On Apr 26, 2016, at 18:27, Andy Farkas wrote: >=20 > On 27/04/2016 02:34, Miroslav Lachman wrote: >> DH wrote on 04/26/2016 17:47: >>>> 5GB of RAM >>>=20 >>> That seems to be an insufficient amount of system ram when employing = zfs. >>>=20 >>> Take a look at this: >>>=20 >>> http://doc.freenas.org/9.3/freenas_intro.html#ram >>=20 >> I know 5GB is not much these days but is memory used for scrubbing a = lot? Because I am satisfied with working performance. The only concern = is slow scrubbing and I am not sure that more memory helps in this case. I don=E2=80=99t expect memory to make a big difference in scrub or = resilver performance. Rememeber the way ZFS uses memory is as both write = buffer and read cache (all in the ARC). So insufficient memory will hurt = real performance but it should not have any real effect on a scrub or = resilver (which are both operations that read all the data that has been = written to the zpool and check it against the metadata for consistency). Scrubs (and resilver) operations are essentially all random I/O. Those = drives are low end, low performance, desktop drives. The fact that the scrub _repaired_ anything means that there was damage = to data. If all of the data on the drives is good, then a scrub has = nothing to repair. What does an `iostat -x 1` show during the scrub ? How about a `zpool = iostat -v 1` ? How hard are you hitting those drives and are they all = really good ? I have seen svc_t values differ by a factor of two among = drives of all the same make and model. Is one drive slower than the rest = ? Perhaps that drive is on the way out.