Re: Draft Mirrored Linux Mini How-to

[Goswin von Brederlow <goswin-v-b@web.de>]

"NeilBrown" <neilb@suse.de> writes:

> On Sat, August 8, 2009 11:11 am, Goswin von Brederlow wrote:
>> Tapani Tarvainen <raid@tapanitarvainen.fi> writes:
>>
>>> On Thu, Aug 06, 2009 at 08:08:47PM -0400, Harold Pritchett
>>> (harold@uga.edu) wrote:
>>>
>>>> Mirrored Linux Mini How-to
>>>
>>> A few quick observations:
>>>
>>>> Install linux on two identical disk drives in such a way that the
>>>> failure
>>>> of either of the drives will allow the system to be recovered without
>>>> any
>>>> loss of data
>>>>
>>>> Both of the drives are partitioned exactly the same:
>>>>      1.  3 primary partitions
>>>>      2.  Partition 1 - size - 1GB format as Linux Raid (fd)
>>>>      3.  Partition 2 - size = real memory size, format as linux swap
>>>> (82)
>>>>      4.  Partition 3 = size = remainder of disk, format as linux raid
>>>> (fd)
>>>
>>> If I read correctly, you are not only leaving swap out of lvm,
>>> you are not mirroring it at all - which would make the system
>>> crash if the swap disk breaks.
>>> Putting swap on lvm would also allow growing it easily as needed.
>>
>> On the other hand don't forget that raid1 is buggy with swap and the
>> page contents might change between writes to the first and second
>> disk. Or has that been fixed?
>
> There is no bug here.  The behaviour is a little unexpected
> but it is perfectly "correct" in that there is never any risk to
> data.
>
> NeilBrown

Disk 1 writes, page is modified, disk 2 writes, page is swapped in
from disk 1, something crashes because old data is swapped in.

Or did I miss something?

MfG
        Goswin