For me one of the best aspects of unRAID is that most disks are always spun down.  When reading only one disk needs to spin up and when writing only two. How will dual parity affect this?

For me one of the best aspects of unRAID is that most disks are always spun down.  When reading only one disk needs to spin up and when writing only two. How will dual parity affect this?

I 'think' from what I have read that it is similar except that there will be 3 disks involved in any write - the data disk and both parity drives.  However if it is really important to you then you need to get official confirmation from LimeTech.

For me one of the best aspects of unRAID is that most disks are always spun down.  When reading only one disk needs to spin up and when writing only two. How will dual parity affect this?

I 'think' from what I have read that it is similar except that there will be 3 disks involved in any write - the data disk and both parity drives.  However if it is really important to you then you need to get official confirmation from LimeTech.

That's correct, and for reads it's the same as single parity.

 

For me one of the best aspects of unRAID is that most disks are always spun down.  When reading only one disk needs to spin up and when writing only two. How will dual parity affect this?

I 'think' from what I have read that it is similar except that there will be 3 disks involved in any write - the data disk and both parity drives.  However if it is really important to you then you need to get official confirmation from LimeTech.

That's correct, and for reads it's the same as single parity.

For reads I did not think parity came into play as only the data disk is read.

 

One slightly linked question is what happens when one drive has failed.  In such a case does the system use all data disks plus one parity to reconstruct the sector for the failed drive or is something more subtle.

This assumes one is not using turbo writes method.

 

When reading from a real data disk only the data disk spins up.

 

When writing to a real data disk only the data drive and both parity drives will spin up in dual parity setup.

 

 

When reading from a failed and simulated data disk when all other drives are fine, all valid data drives and at least one parity drive will be spun up in dual parity setup.

 

When reading from a failed and simulated data disk when there is a second data drive failed, all valid data drives and both parity drives will be spun up in dual parity setup.

 

If I remember correctly with one failed disk both paritys are used together with all data disks, don’t know if it's a beta thing.

This assumes one is not using turbo writes method.

 

When reading from a real data disk only the data disk spins up.

 

When writing to a real data disk only the data drive and both parity drives will spin up in dual parity setup.

 

 

 

Awesome!  This is what I care about.

 

thank you all for your speedy replies.

If I remember correctly with one failed disk both paritys are used together with all data disks, don’t know if it's a beta thing.

 

Hrm, i wonder what happens if P and Q dont match at that point, meaning P calculates it as 0 but Q calculates it to be 1.

 

It might spin both disks just because the code path might be less complex that way even though technically the other parity disk isnt needed.