From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: "bitmap" line in /proc/mdstat Date: Fri, 14 Oct 2016 07:53:02 -0400 Message-ID: <8922e2e1-b612-fa32-6932-9f4158f52fe6@turmel.org> References: <5800AE09.70608@bluewin.ch> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5800AE09.70608@bluewin.ch> Sender: linux-raid-owner@vger.kernel.org To: Ramon Hofer , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 10/14/2016 06:06 AM, Ramon Hofer wrote: > From what I was reading [1,2] it is useful for faster rebuilds. > But why is it not present for md[1234] as I used the same command to > create these RAIDs? > Is it only possible for the last of the linear devices, or is it only > used for almost empty devices, or was the bitmap introduced in a recent > update? Bitmaps have been available for a long time, but including them on a new array by default is recent. They are most useful if a device is unexpectedly disconnected but otherwise OK. mdadm --re-add will allow that device to rejoin the array and only the missing data (tracked by the bitmap) will have to be written to sync it up. > I wonder if I should and could add a bitmap for the other devices as well? There is a performance hit, so it should be considered on a case by case basis. Phil