From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pigeon.gentoo.org ([208.92.234.80] helo=lists.gentoo.org) by finch.gentoo.org with esmtp (Exim 4.77) (envelope-from ) id 1SoJfA-0007ci-Tz for garchives@archives.gentoo.org; Mon, 09 Jul 2012 19:30:29 +0000 Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 8A5F2E06F4; Mon, 9 Jul 2012 19:30:15 +0000 (UTC) Received: from mail-bk0-f53.google.com (mail-bk0-f53.google.com [209.85.214.53]) by pigeon.gentoo.org (Postfix) with ESMTP id 2AB32E06BF for ; Mon, 9 Jul 2012 19:28:48 +0000 (UTC) Received: by bkwj4 with SMTP id j4so4851798bkw.40 for ; Mon, 09 Jul 2012 12:28:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=83ndbOen2d4LRzhNAPb9X82ARPB2mZhxZ83ZgkGDlaw=; b=UcOIeO+KG0VOsbm1U09ZNESfdJDQWu09PvB0Gk5Vy/xZFnZ0sNozR7XAOTEs7D6imB WwC8kyWFrd8PB0yRDaU6yCZ/WtW+saoZ1cWDTN2BDTlzfEa0UV9yRMnmKgwahzYCboVT oXDG7iFctx954EH/3JACJg1qLFZABqFP6eVcwvNZXC4y0boeSF2DxtZkO5+s5hzJ5MV8 djVNjDFFUG56mSSpcDyqv7weHgrKoQQ4Cg3do+omUbvY79pXTW2ej/n40hYSiLoDSVq8 hvhpJT3l63Q05LFmmXiDJvB9zcrvn3l8Y6yk+Bpo4ouoV4KKGOtagK0dpE+7EWainq33 lJPw== Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 Received: by 10.204.155.66 with SMTP id r2mr17731806bkw.131.1341862128237; Mon, 09 Jul 2012 12:28:48 -0700 (PDT) Received: by 10.204.149.23 with HTTP; Mon, 9 Jul 2012 12:28:48 -0700 (PDT) In-Reply-To: <4FFB2D0F.8090606@binarywings.net> References: <4FFB1443.4090500@gmail.com> <4FFB2D0F.8090606@binarywings.net> Date: Mon, 9 Jul 2012 15:28:48 -0400 Message-ID: Subject: Re: [gentoo-user] OT: HW-raid1 & SSD? From: Michael Mol To: gentoo-user@lists.gentoo.org Content-Type: text/plain; charset=UTF-8 X-Archives-Salt: c04d286e-6ce4-4a45-a5b9-5762911ef873 X-Archives-Hash: 9465b18ce9e99bbb60096ee2cc9d311e On Mon, Jul 9, 2012 at 3:12 PM, Florian Philipp wrote: > Am 09.07.2012 19:26, schrieb Jarry: >> Hi, >> >> I'm building small server for VPS-hosting purpose (not decided >> yet, probably KVM or ESXi). Althought it is "non production", >> reliability is still issue for me. I'm considering using two >> small SSD (ie. Intel 313, 24GB, SLC) in hw-raid1 (Adaptec 3805) >> just for hypervisor, and 2xHDD/raid1 for VPS. >> >> I started looking for info on internet but results are not >> conclusive. Opinions vary from "no problem, use SSD&raid1" >> to "using SSD in raid is not recommended no matter if it is >> SW or HW". Mostly missing trim-command is mentioned as reason >> for not using SSD in any raid. >> >> Does anyone have any experience with SSD in raid (SW or HW)? >> Is it safe to use it on server? >> >> Jarry > > I don't think trim is currently supported in mdaid. AFAIK dmraid > supports it as long as the RAID controller plays along. I'm unsure about > LVM mirrors. > > But trim is not your only issue: mdraid and LVM as well as most (all?) > hardware RAIDs will mirror all blocks from one disk to the other when > you assemble the RAID-1. This means that all blocks on your second SSD > will immediately be marked dirty which incurs a significant performance > penalty. Well, yes and no. Yes, there will be a performance penalty from having all the blocks marked dirty. But this would eventually happen anyway! On the other hand, once all blocks are marked dirty, you have performance _stability_. If you're in a position to care about predictive performance metrics, stability is quite useful. -- :wq