Fwd: mounting component device of RAID1 with internal bitmap

[CoolCold <coolthecold@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2102 bytes --]

Just to share this with list.


---------- Forwarded message ----------
From: Doug Ledford <dledford@redhat.com>
Date: Thu, Apr 1, 2010 at 11:34 PM
Subject: Re: mounting component device of RAID1 with internal bitmap
To: CoolCold <coolthecold@gmail.com>


On 04/01/2010 03:25 PM, CoolCold wrote:
> On Thu, Apr 1, 2010 at 10:39 PM, Doug Ledford <dledford@redhat.com> wrote:
>> On 04/01/2010 02:26 PM, CoolCold wrote:
>>> On Thu, Apr 1, 2010 at 10:14 PM, Doug Ledford <dledford@redhat.com> wrote:
>>>> On 04/01/2010 01:47 PM, CoolCold wrote:
>>>>> Hello!
>>>>> For raid1 array with metadata 0.90 it is possible to mount component
>>>>> (let's say /dev/sda1) as usual FS, fix smth, /etc/fstab for example,
>>>>> unmount and then assamble arary.
>>>>
>>>> At which point you have just corrupted your array.
>>> I've did such operation several times and it worked fine..I'll do some
>>> checks and report later.
>>
>> Because you got lucky.  When you do this, you make the different members
>> of the raid array disagree on the contents of whatever file you
>> modified.  Depending on which disk the kernel reads from, you will get
>> either the new or the old contents of the file.  Any time you mount a
>> component device and modify it, you *must* force a resync from that
>> component to all other components or you *will* have a corrupt array.
>> When that corruption will crop up to bite you in the ass is up to random
>> chance.
> Ah, ofcourse recync is ok , i wanted to know will this break _raid_
> (eg erase some metadata) itself, not actual data on top of it. For 0.9
> it is said in man that it stored at the end of device, but what about
> bitmaps? are they at the end too ?

The bitmaps are outside of the regular filesystem area, so they can't be
harmed by mounting the filesystem.


--
Doug Ledford <dledford@redhat.com>
             GPG KeyID: CFBFF194
             http://people.redhat.com/dledford

Infiniband specific RPMs available at
             http://people.redhat.com/dledford/Infiniband




-- 
Best regards,
[COOLCOLD-RIPN]

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 198 bytes --]