From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Peter Sangas" Subject: RE: "bitmap" line in /proc/mdstat Date: Fri, 14 Oct 2016 09:08:25 -0700 Message-ID: <003401d22635$32b7bc70$98273550$@wnsdev.com> References: <5800AE09.70608@bluewin.ch> <8922e2e1-b612-fa32-6932-9f4158f52fe6@turmel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <8922e2e1-b612-fa32-6932-9f4158f52fe6@turmel.org> Content-Language: en-us Sender: linux-raid-owner@vger.kernel.org To: 'Phil Turmel' , 'Ramon Hofer' , linux-raid@vger.kernel.org List-Id: linux-raid.ids Can you quantify the performance decrease and if rebuild time is not as important as performance how does one remove the bitmap? Thank you, Peter -----Original Message----- From: Phil Turmel [mailto:philip@turmel.org] Sent: Friday, October 14, 2016 4:53 AM To: Ramon Hofer; linux-raid@vger.kernel.org Subject: Re: "bitmap" line in /proc/mdstat 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 -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html