bootable ext. USB SSD for backup

[Martin S. Weber]

On 03/16/17 21:37, Ralf Mardorf via freebsd-questions wrote:
> On Thu, 16 Mar 2017 21:11:53 +0100, Martin S. Weber wrote:
>> Toshiba is clearly underselling the  disk.
>
> I don't think so, I suspect that some bytes are reserved to compensate
> borked memory locations.
>
>   [rocketmouse at archlinux ~]$ sudo smartctl -a /dev/sda | head -9
>   smartctl 6.5 2016-05-07 r4318
>   [x86_64-linux-4.9.13-rt12-1-rt-persianrug] (local build) Copyright (C)
>   2002-16, Bruce Allen, Christian Franke, www.smartmontools.org
>
>   === START OF INFORMATION SECTION ===
>   Device Model:     TOSHIBA-TL100
>   Serial Number:    Y69B703NKKEU
>   LU WWN Device Id: 5 00080d c0061b7c8
>   Firmware Version: SBFZ10.3
>   User Capacity:    240,057,409,536 bytes [240 GB]
>
> GParted mentions 223.57 GiB * 1024 * 1024 = 234,430,136.32 bytes.
> MBR, file system entries might take some space, too. OTOH the complete
> capacity shouldn't shrink ;).

bc is your friend:
223.57*2^30 (actually GiB, not 1024*1024 which is MiB)
240056459591.68 and compare to your
240057409536 from above.

The difference is slightly less than a MiB:
scale=3
(240057409536 - 223.57*2^30)/2^20
.905

Can we stop this excursion now? AFAIK the extra bytes which are to be 
used as reserve aren't actually reported by the drive.

Regards