From owner-freebsd-fs@FreeBSD.ORG Sun Oct 16 18:10:05 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 54A581065673 for ; Sun, 16 Oct 2011 18:10:05 +0000 (UTC) (envelope-from daniel@digsys.bg) Received: from smtp-sofia.digsys.bg (smtp-sofia.digsys.bg [193.68.3.230]) by mx1.freebsd.org (Postfix) with ESMTP id CECC18FC12 for ; Sun, 16 Oct 2011 18:10:04 +0000 (UTC) Received: from [192.92.129.101] ([192.92.129.101]) (authenticated bits=0) by smtp-sofia.digsys.bg (8.14.4/8.14.4) with ESMTP id p9GI9rLe026908 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NO); Sun, 16 Oct 2011 21:10:00 +0300 (EEST) (envelope-from daniel@digsys.bg) Mime-Version: 1.0 (Apple Message framework v1251.1) Content-Type: text/plain; charset=us-ascii From: Daniel Kalchev In-Reply-To: <4E9B1C1E.7090804@gmail.com> Date: Sun, 16 Oct 2011 21:09:53 +0300 Content-Transfer-Encoding: quoted-printable Message-Id: <14628DFB-AA3E-4D2D-9D4F-723B6327B6C0@digsys.bg> References: <4E9AE725.4040001@gmail.com> <169E82FD-3B61-4CAB-B067-D380D69CDED5@digsys.bg> <4E9B1C1E.7090804@gmail.com> To: "Luchesar V. ILIEV" X-Mailer: Apple Mail (2.1251.1) Cc: freebsd-fs@freebsd.org Subject: Re: [ZFS] Using SSD with partitions 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: Sun, 16 Oct 2011 18:10:05 -0000 On Oct 16, 2011, at 21:02 , Luchesar V. ILIEV wrote: > On 16/10/2011 19:17, Daniel Kalchev wrote: >> Therefore, with ZFS v28, adding ZIL does not introduce any more risk >> to your data. >=20 > I might be wrong in my interpretation, but from what I remember, when > the power goes down, an unprotected SSD is likely to lose _more_ data > than simply its write buffers -- that's quite unlike a hard-drive. So > much, in fact, that the whole ZIL might become corrupted (and that's > potentially way more data than any device cache). The real risk with low-grade "unprotected" SSDs is that the SSD may well = become damaged, sometimes beyond repair. It is the same risk with SSDs or with magnetic drives. If the drive lies = to the OS that it has safely written data -- then data will be lost. = Thing is, we know what a cheap HDD is. Most SSDs however lie, because = otherwise they will offer very poor write performance. ZIL is not about RAM. ZIL is for low latency synchronous writing. It = does not matter how much RAM do you have -- it will not help if you have = heavy synchronous writing (of small records). =20 Anyway, as it was mentioned -- with moderate activity on the pool, it is = not problem to use the same SSD for boot/ZIL/L2ARC. Daniel=