From owner-freebsd-fs@freebsd.org Mon Aug 10 14:04:15 2015 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 22FED99E5B3 for ; Mon, 10 Aug 2015 14:04:15 +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 03627AAB for ; Mon, 10 Aug 2015 14:04:14 +0000 (UTC) (envelope-from paul@pk1048.com) Received: from mail.thecreativeadvantage.com ([96.236.20.34]:56403 helo=mbp-1.thecreativeadvantage.com) by cpanel61.fastdnsservers.com with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.85) (envelope-from ) id 1ZOngN-0028Ny-L3; Mon, 10 Aug 2015 09:04:07 -0500 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Subject: Re: Urgently need some help solving lost space due to snapshots during receive op From: PK1048 In-Reply-To: <55C863DE.3000200@digiware.nl> Date: Mon, 10 Aug 2015 09:20:35 -0400 Content-Transfer-Encoding: quoted-printable Message-Id: <43B00232-46B7-4B96-B80C-D0111C6D8DA2@pk1048.com> References: <55C82BCD.2050404@herveybayaustralia.com.au> <55C863DE.3000200@digiware.nl> To: FreeBSD Filesystems X-Mailer: Apple Mail (2.1878.6) 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-Source: X-Source-Args: X-Source-Dir: X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 10 Aug 2015 14:04:15 -0000 On Aug 10, 2015, at 4:42, Willem Jan Withagen wrote: > Last number I remember as sensible maximum fill level is around 70%. > If you go over it, your system is going to be busy with ZFS = bookkeeping > instead of data storage. Fortunately or not, that number is _very_ dependent on your specific = data and how it is loaded. If it is static data, loaded once and not = modified, you can run a much higher % Used, for lots of changes on an = ongoing basis you need much more free space. The issue is that since ZFS = is Copy on Write, every write (even a modification to an existing file = or disk block) needs to find space. ZFS tries to reduce fragmentation. = As the zpool gets more and more full it takes longer and longer to find = the best possible location to put the new write. It also becomes harder = and harder to find contiguous blocks to put the new write into. The = existence of snapshots makes this problem even worse, as previously = written data is not cleared until the snapshot is destroyed.