From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Eric D. Mudama" Subject: Re: SSD - TRIM command Date: Wed, 9 Feb 2011 02:05:22 -0700 Message-ID: <20110209090522.GA8632@bounceswoosh.org> References: <4D517F4F.4060003@gmail.com> <4D5245DF.4020401@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Return-path: Content-Disposition: inline In-Reply-To: <4D5245DF.4020401@hardwarefreak.com> Sender: linux-raid-owner@vger.kernel.org To: Stan Hoeppner Cc: maurice , Roberto Spadim , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, Feb 9 at 1:44, Stan Hoeppner wrote: >maurice put forth on 2/8/2011 11:37 AM: >> On 2/7/2011 1:07 PM, Roberto Spadim wrote: >>> hi guys, could md send TRIM command to ssd? using ext4 discart mount option? >>> if i mix ssd and hd, could this TRIM be rewrite to non TRIM compatible disks? >>> >> I have read that using md with SSDs is not a great idea: >> Form the Fedora 14 documentation: > >Using any RAID level but pure striping with SSDs is a bad idea, for the exact >reason in that documentation: excessive writes. If I mirror two SSDs, and write 1 unit of data to the mirror, each element of the mirror should see 1 unit of write. How does this perform excessive writes, compared to the same workload applied to a single SSD? I agree that in aggregate we've now done 2 units worth of writes, however, in a mirror case, we're protecting against both whole-device failure and single-sector failure modes, so hardly seems like a bad idea in all applications. -- Eric D. Mudama edmudama@bounceswoosh.org