From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ve0-f178.google.com ([209.85.128.178]:44167 "EHLO mail-ve0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750849AbaFZUq6 (ORCPT ); Thu, 26 Jun 2014 16:46:58 -0400 Received: by mail-ve0-f178.google.com with SMTP id oy12so4394910veb.9 for ; Thu, 26 Jun 2014 13:46:57 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <56CE0D0C-EE96-4CBC-B7CB-FC42CA1B01DF@colorremedies.com> References: <2316027.LZEnVG8laK@xev> <6CA8020B-EB92-4A44-8AA5-3F69709F81F2@colorremedies.com> <53A6DDAD.8070804@chinilu.com> <99AD3EFE-AF9A-44A1-912E-07B1E934239B@colorremedies.com> <56CE0D0C-EE96-4CBC-B7CB-FC42CA1B01DF@colorremedies.com> Date: Thu, 26 Jun 2014 22:46:57 +0200 Message-ID: Subject: Re: btrfs on whole disk (no partitions) From: Imran Geriskovan To: Chris Murphy Cc: Btrfs BTRFS Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 6/26/14, Chris Murphy wrote: > On Jun 25, 2014, at 7:01 AM, Imran Geriskovan >> There are SSDs with 4K, 8K block/page sizes and >> 512K, 1M, 1.5M Erase block sizes. >> Partitions should be aligned with Erase blocks. > That sounds plausible, but the FTL in the consumer SSD's most all of us are > buying isn't going to give you any assurance it's actually writing with such > boundaries in mind. You may have partition 1 start on LBA 2048, which is 1MB > aligned, but as soon as you're writing data to LBA 2048 through say LBA > 2560, for all you know that write actually ends up in pages that are located > in the first and second erase blocks; or maybe all of it's in the 8th erase > block. The OS side of things we don't have insight or control over this. 8 Logical blocks (Not 8 Erase blocks) makes a 4K Physical block. (a) Basic principle is to align with "Physical blocks" ("Pages" for SSDs). (b) For SSDs, aligning with Erase blocks (512K, 1M, 1.5M) also satisfy (a) Regards, Imran