Protection information and power loss/write failures

Matthew Jacob mj at feral.com
Mon Mar 3 09:47:58 PST 2014


* From the T10 Reflector (t10 at t10.org), posted by:
* Matthew Jacob <mj at feral.com>
*
On 3/3/14 9:34 AM, Gerry Houlder wrote:
> Power loss can cause lots of issues, including have a logical block 
> contain data that is part old data and part new data. If the last part 
> of the logical block has the "old data", it may also have "old 
> protection information", so a subsequent read attempt of the new data 
> plus old data plus old protection information would result in a 
> protection check error.
>
> Most real implementations of storage devices attempt to prevent having 
> a single logical block have mixed data like this but they are not 
> always successful. The intent of the standard is that a host should 
> assume any outstanding write command that did not complete before a 
> power loss occurs should be retried in its entirety after power is 
> restored.
>
Note that recovery mechanisms, if any, are device specific. Devices that 
can safely retry can be retried. Devices that cannot, e.g., tape or 
optical media (in some cases) cannot.
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