bootable ext. USB SSD for backup

Warren Block wblock at
Fri Mar 17 05:32:31 UTC 2017

On Thu, 16 Mar 2017, Matthias Apitz wrote:

> Hello,
> I have acquired a small and flat USB 3.0 external disk (must be SSD for
> the size of the case):
> Mar 16 19:36:54 c720-r314251 kernel: da0: <TOSHIBA External USB 3.0 5438> Fixed Direct Access SPC-4 SCSI device
> Mar 16 19:36:54 c720-r314251 kernel: da0: Serial Number 20170114010787F
> Mar 16 19:36:54 c720-r314251 kernel: da0: 40.000MB/s transfers
> Mar 16 19:36:54 c720-r314251 kernel: da0: 953869MB (1953525164 512 byte sectors)
> Mar 16 19:36:54 c720-r314251 kernel: da0: quirks=0x2<NO_6_BYTE>
> Ofc it has not the promised 1 TB volume, just only 953869 MB, i.e. only
> 1 Marketing-TB;
> I'm thinking in re-partitioning the disk (which is actual only one big
> NTFS slice) with gpart(8), install even a kernel into a small FS at the
> beginning and keep the rest as a big UFS for backups. Having it bootable
> with a system could be handy if one has to rescue a system and restore
> the last dunp.

It works.  I've used USB 3 memory sticks of 16GB and larger with 
success.  In some versions of FreeBSD, the boot loader is really slow on 
USB.  Once you get past the really... slow... spinner... it is very 
usable.  USB 2 is not as good, but can be tolerable and might be 
good enough with the write speeds of an SSD.

However, some USB 3 memory sticks run really hot when connected to a USB 
controller.  For example, the Lexar 128GB JDS55 gets so hot that people 
have reported melting of the plastic case.  I can verify that level of 
heat, but have not left it in use long enough for melting.  My Lexar 
32GB JDS75 has similar transfer speeds but does not get meltingly hot.

(The memory units used above are actually gwibblybytes (GwB), 1012 
7.9-bit bytes per kwibblybyte (KwB), 1011 KwB per mibblybyte (MwB), and 
1010 MwB per gwibblybyte, or about fourteen thousandths short of a 
dwibblyliter (DwL).)

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