dump/restore, how to reduce slice size

[Damien Fleuriot]

On 9/29/11 10:09 PM, Jerry McAllister wrote:
> On Thu, Sep 29, 2011 at 10:36:38PM +0300, ??????? ??????? wrote:
> 
>> Hi, Freebsd-questions.
>>
>> # df -h
>> Filesystem     Size    Used   Avail Capacity  Mounted on
>> /dev/ad4s1a      2G    206M    1.6G    11%    /
>> devfs          1.0k    1.0k      0B   100%    /dev
>> /dev/ad4s1e    3.9G     13M    3.6G     0%    /tmp
>> /dev/ad4s1f     40G     25G     12G    67%    /usr
>> /dev/ad4s1d     31G    3.6G     24G    13%    /var
>> procfs         4.0k    4.0k      0B   100%    /proc
>> /dev/ad2s1f     39G     25G     10G    71%    /mnt
>> devfs          1.0k    1.0k      0B   100%    /var/named/dev
>>
>>
>> as you can see /dev/ad4s1f is 40G and /dev/ad2s1f is 39G
>> but on ad4s1f only 25G used.
>>
>> How can I dump /dev/ad4s1f and restore it on /dev/ad2s1f?
>>
>> These commands:
>> #mount /dev/ad2s1f /mnt
>> #cd /mnt
>> #dump -0Lf - /usr | restore -rf -
>> does not help, because of ad2s1f does not have space to restore
>> 'end of ' /dev/ad4s1f.
>>
>> May help any?
> 
> Well, you are going to have difficulty putting 50 GB on a 39 GB partition.
>    (25GB + 25GB = 50GB).
> It won't work.
> 
> You could try compressing the dump, but dump files do not tend
> to compress well and even if you got a 50% compression, you would
> still be really close to overfill.
> 
> Probably you need to go to the store and get a nice big USB drive
> and slice and partition it in to a bunch of 50 GB partitions and
> pipe your dump to a restore in those partitions on that drive.
> You can round-robin your backups to those USB partitions.
> 
> My backup to a USB hard drive just saved me the beginning of
> this week when the old machine died of heat prostration.
> 


Dump is supposed to take only the used space.

@OP, refer the following link for correct dump/restore syntax:
http://www.wonkity.com/~wblock/docs/html/backup.html#_tt_dump_tt_with_compression