From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Landman Subject: Re: Is this expected RAID10 performance? Date: Sun, 09 Jun 2013 20:05:35 -0400 Message-ID: <51B5184F.9040707@gmail.com> References: <51B47088.4000501@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Steve Bergman Cc: Ric Wheeler , Linux RAID List-Id: linux-raid.ids On 06/09/2013 04:06 PM, Steve Bergman wrote: > Google for "ZFS and zeroes" you surely noticed that many of the s/ZFS/xfs/ [...] > Saying that "you can lose data with any filesystem" is true... but > evasive, and misses the point. One could say that speeding down the Er ... no. If you insist upon absolute "guarantees" in *any* file system, then mount it with a sync option, so writes don't return until they are committed to disk, turn off all write caching on the drive, and turn off any other write caching throughout the system. And if you believe that this *guarantees* your data integrity, I'd suggest staying away from real estate sales people in Florida. You have to understand what is *guaranteed* and what is not. Where bugs can hit (yes, bugs in the stack can tank a file system). You can get corruption *anywhere* along the pathway from CPU to disk. Anywhere. Even with ECC memory, checksums, etc. Have a good long gander at this http://www.snia.org/sites/default/files2/SDC2011/presentations/monday/WilliamMartin_Data_Integerity.pdf and other articles on T10 DIF. Understand that file systems do not give you guarantees. If you must provide a guaranteed non-data lost system, then you need to engineer a resilient system below the file system itself. At the file system level, you need to use options which give you the highest probability of surviving a data loss event. Understand that you *will* lose data irrespective of what file system you have on there. Its the best practices that you may or may not choose to implement that matter here, in terms of how impactful this data loss will be. If you don't know how to use XFS safely, thats fine. Its a very good file system, I've personally used it since IRIX days (when I was at SGI). Many very large organizations swear by it. Few would run without it. But if you prefer something else, fine. Just understand you are going to lose data with the other file system as well. Denying that this is possible is not a viable strategy to ameliorate the damage from the loss, and fundamentally, your focus should be on risk amelioration with respect to your choices, not arguing with the development team over your choices. Now, please, back to your regularly scheduled IO RAID system ...