[RndTbl] Open Source Backup/cloning to USB HDD

Adam Thompson athompso at athompso.net
Wed Oct 28 01:28:28 CDT 2009

On Wed, Oct 28, 2009 at 01:10, Peter O'Gorman <peter at pogma.com> wrote:

> On 10/27/2009 09:38 PM, Adam Thompson wrote:
> > reallocate bad sectors on WRITE, and *not* on read.  The *destructive*
> > SMART "Long" test causes every sector to be re-written, which will
> I don't believe the SMART long test is destructive, why do you think so?

Sorry, I wasn't clear enough in my original posting.

The regular SMART "Long" test is *not* destructive.

Some HDDs - there's no pattern than I can discern to tell which, other than
reading the documentation - offer an additional, *non-standard* destructive
test.  Some of *those* HDDs appear to invoke the same function as "low-level
format", since both are essentially equivalent processes.  Sector remapping
takes place as usual during either command.

Generally speaking, SCSI, FC and SAS devices should always support a
low-level format command, per ANSI T13.  IDE and SATA devices may or may not
support a low-level format command.  The SMART specification (per ANSI T13)
is extensible, and specifies a *minimum* level of functionality; some
vendors - at least in certain models - implement more than minimum required
functionality.  It seems to me that models sold as OEM equipment to server
and storage appliance vendors often implement extra functionality, probably
at the request of vendors like NetApp, EMC, Dell, HP, etc.  Since most
storage vendors now offer cheap(er) SATA storage options for their arrays,
some so-called "desktop" models will also benefit from this.

The only way to be certain is to read the technical documentation for your
particular drive, which will tell you precisely what commands the drive
supports.  I'm not talking about the user manual; note that some drives do
not appear to have any such documentation - in which case you can probably
assume they don't support anything beyond the minimum required feature set.

-Adam Thompson
<athompso at athompso.net>
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