[CentOS] mkswap, lvm and bootbits sectors

Peter Kjellström cap at nsc.liu.se
Tue Mar 13 13:08:20 EDT 2012


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.

You could write a meg of zeroes to the device first and see if the mkswap 
warning goes away.

/Peter

> (If that matters, the swap is intended for a virtual machine, and
> the host where I am using mkswap is a CentOS-6 server.)
> 
> Thanks,
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