[CentOS] mkswap, lvm and bootbits sectors

[m.roth at 5-cent.us]

Peter Kjellström wrote:
> On Tuesday 13 March 2012 13.41.53 Philippe Naudin wrote:
>> Hello,
>>
>> I am confused by a warning from mkswap :
>>
>> When making a swap on a LVM volume, I see the following warning :
>>   mkswap: /dev/vg_SDB1/swap_test6_64: warning: don't erase bootbits
>>   sectors on whole disk. Use -f to force.
>>   Setting up swapspace version 1, size = 1048572 KiB
>>
>> Is it safe to use mkswap -f in this case ?
>
> I'd say it's safe but why do it?
>
> What likely happened is that the lv you ran mkswap on contained a valid
> partition table (or at least boot signature). Out of paranoia mkswap left
> the first block alone. So what you could gain is maybe another 512 byte in
> swapspace by adding -f.
<snip>
Are you making swap from a logical partition, or a swapfile? If the
former, perhaps recreating the partition might help.

       mark