Re: Draft Mirrored Linux Mini How-to

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

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?

> Another point is that sometimes it is useful to have multiple
> partitions separately mirrored and then combined with lvm:
> it allows things like changing the raid configuration from
> two-disk raid1 to three-disk raid5 without moving data
> via backup and yet avoiding windows of vulnerability
> to single-disk failure during the transition.
> (Perhaps not common enough to be worth mentioning here,
> but I've found it useful.)

You can transform raid1 to raid5 without loss of redundncy so I don't
quite see what you mean here.

MfG
        Goswin