Re: fstrim on newly created filesystem tries to discard data beyond the last sector of a device

[Bernd Schubert <bernd.schubert@fastmail.fm>]

On 11/24/2014 09:03 PM, Lutz Vieweg wrote:
> On 11/24/2014 08:43 PM, Bernd Schubert wrote:
>>> Then there's another idea: The device is a SATA SSD, but attached
>>> to a SAS2 expander chip on the backplane of the server (LSI SAS2X28)
>>> which in turn is connected to a LSI SAS HBA 9207-4i4e.
>>> could maybe, just maybe, the TRIM command be modified wrongly
>>> on its way through these / their respective drivers?
>>
>> Yeah, it is a known issue with LSI firmware.
>>
>> http://osdir.com/ml/dm-devel/2013-09/msg00126.html
> 
> I must admit that I have difficulties understanding what this
> email thread is ultimately telling: Does it mean LSI firmware
> actually tampers with TRIM commands such that they would discard
> other ranges than those intended? (In which case using TRIM
> over any such LSI device would be very dangerous.)
> Or does is mean the capabilities of some SSDs to discard data
> are mis-reported? And if so, in the sense that the kernel might
> not be able to discard data at all, or in the sense that data
> is discarded, but the kernel sends additional commands that the
> device cannot understand?
> 
> After all, if it's just an annoying error message that I can
> ignore, I wouldn't mind. But if TRIM via LSI means "data loss",
> I would of course have to take measures against this...
> 

It just tries to trim one sector more than the device actually has. So
as far as I can tell it is harmless.