RFC: Project geom-events

[Alexander Motin]

Miroslav Lachman wrote:
> Lev Serebryakov wrote:
>>    One thing is missed from software RAIDs is spare drives and state
>> monitoring (yes, I know, that geom_raid supports spare drivers for
>> metadata formats which supports them, but it not universal solution).
> 
> I am still missing one thing - dropped provider is not marked as failed
> RAID provider and is accessible for anything like normal disk device. So
> in some edge cases, the system can boot from failed RAID component
> instead of degraded RAID. This can cause data loss or demage.

To reliably boot from RAID array, you need help from some RAID BIOS.
While booting from correctly working gmirror is possible, it may not be
reliable when array is degraded. That is one of the main benefits of the
graid, comparing to gmirror -- cooperation with RAID BIOS.

Ability to track failed devices also depends on specific metadata
format. For example, for Intel RAID BIOS, metadata stored on each disk
include information about all other disks used now. As result, if some
disk fails and system is unable to update it's metadata any more, that
information can still be stored on other devices to prevent disk
resurrection in most cases.

-- 
Alexander Motin