Regarding Parity protested Array and a faulty sector.

[MrZaZ]

Hello,

I am a new user to unRaid and have tried to read through all info regarding array and parity

but there is one thing I have not managed to understand.

 

With a normal disk, especially NAS targeted disks, you have built in recovery functions

to detect and move possible bad sectors to other part of the disk without loss of data

and then mark that sector as bad to not be used any longer.

This works ok in normal usage of a disk as the disk keeps tracks of bad sectors and
tells OS not to use the bad.  It will not treat the whole disk as bad even if this happens

even if it is advisable to start looking into replacing the disk eventually.

 

But, what happens in a unRaid array with parity disk enabled if this happens?

As parity is calculated in sector 0 on all disk then if sector 0 in disk 2 is by the HDD

decided to be dodgy and the HDD decide that it want to move data to another sector

position and then mark sector as bad not to be used.

 

Will unRaid detect this as bad disk then even if the whole disk is not bad but just one

sector and that the hdd is handling this by error recovery?

 

Could someone explain exactly what will happen in the explained scenario?

I really want to know that the unRaid with parity would be stable enough to

handle when a HDD performs error recovery with data move to new sector

and mark sector as bad not to be used but still not bomb out the whole array

or mark the whole disk as bad as it really isn’t. Only a sector bad and data moved.

 

Best regards

Dan Lundqvist

Stockholm, Sweden

 

 

[JorgeB]

When bad sectors are re-allocates by the disk's firmware they keep using the old LBA, it's transparent to any OS.

[MrZaZ]

4 hours ago, johnnie.black said:

When bad sectors are re-allocates by the disk's firmware they keep using the old LBA, it's transparent to any OS.

Ok, so from UnRaid point of view, sector 0 is always sector 0 towards UnRaid OS regardless where it is physically located on the low level on the platter.
LBA Sector 0 will remain the same data regardless if disks firmware decides to physically move the content to a different low level sector position as part of low level HDD error correction ?

 

If so, then it should be ok as from UnRaid the data parity will remain the same as it's sector 0 is unchanged. Only moved on low level physically on the disk.

 

Thanks for the clarification. :-)

 

//Dan Lundqvist

[JorgeB]

Correct.

[sota]

We haven't had OS access to actual physical sectors since the MFM/RLL drive days.

[MrZaZ]

1 hour ago, sota said:

We haven't had OS access to actual physical sectors since the MFM/RLL drive days.

Touche.... 😂

RLL...  That was the time... 

Along with ISA bus MB with manual IRQ assignments and IRQ collisions. 

NOT one thing that I look back at with joy... Hehehe 

 

386/486 timeframe... 

 

Danne

[sota]

I come from a time when we used to screw with the signaling on floppy drives of an APPLE ][+ to add extra sectors, and to do copy protection.

 

And those days weren't all bad... in fact in a lot of ways they were much easier.

[MrZaZ]

2 hours ago, sota said:

I come from a time when we used to screw with the signaling on floppy drives of an APPLE ][+ to add extra sectors, and to do copy protection.

 

And those days weren't all bad... in fact in a lot of ways they were much easier.

Yes. Started with VIC20, continued doing  a lot with C64. Then off to PC with Lantastic coax network with a 486dx2/50 running OS2 with BBS in the background and a filserver in a 386sx25 via Lantastic. That was the times... 🙂

 

/Danne

[sota]

Throw in a HeathKit H-88 (ah... the smell of flux core solder during assembly) and a TRS-80 Color Computer, and you just described a good chunk of my childhood.

[MrZaZ]

22 minutes ago, sota said:

Throw in a HeathKit H-88 (ah... the smell of flux core solder during assembly) and a TRS-80 Color Computer, and you just described a good chunk of my childhood.

🙂😁... 

Still have my old O.G C64 in a cardboard box in the next room. With a Floppy 1541 drive... Hehe

Dannd