help creating new gmirror > 2TB

Frank Leonhardt frank2 at
Thu Aug 31 14:18:01 UTC 2017

On 31/08/2017 02:37, JD wrote:
> I thought that hdparm could work with the firmware to set the sector 
> size.
> Not sure on this because hdparm has gone through a lot of modifications
> over the years.

In the good old days, a sector was a sector! Fixed in to the disk by 
drilling a hole and shining a light through it as it spun past a sensor.

IDE (aka S/ATA drives lie a LOT about what they're really doing. If you 
want them to pretend their sectors are 512b they will. But on the 
hardware they're fixed at 4K, so they read 4K in and throw away 3.5K. It 
gets bad if your OS is reading one sector at a time and the drive isn't 
caching it; and as the FS block size is unlikely to be 512b it gets 
fraught quite quickly.

As you need an inter-sector gap and each sector has an ECC overhead 
that's not proportional to it's length, having larger physical sectors 
also means more of the disk is used for data and less for padding and 

Regards, Frank.

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