Hi,

 

Old time unRaid lurker, new owner of an unRaid server.

1st time parity check running, rather slow than expected.

Do you think that a data copy and preclear running got to do with that? 

Anyway, if I stop the array, add a new precleared drive to it, then start the array,

will parity check continue from it's current position or start all over?

 

Also the same question regarding adding of a new cache pool (4 precleared disks).

 

Thanks.

If canceled parity check will always start from the beginning.

 

Preclear should not be a problem, but not really a good idea to copy data during a parity check, it will slow down both things considerably.

1st time parity check running, rather slow than expected.

How slow is it and what did you expect?

How slow is it and what did you expect?

 

Started the array for the 1st time, and shortly after the data copy.

6TB parity check at 18.8%, 4TB copy at 68% percent.

Expected the parity (only 1 data disk in the array) to be faster.

Actually was surprised with the parity check because both disks are precleared.

Sounds like you're running a parity SYNC ... not a CHECK.    Simlar, but not the same ... the sync is the initial calculation of parity;  a check is confirming that all's still well with parity.

 

In either case, writing to the array while the parity operation is in progress is NOT a good idea.  This causes excessive thrashing of both the disk being written to and the parity disk, as the heads will continually move between the current location of the parity sync/check and the area of the disk where data's being written to.    The seek and latency delays involved in every movement of the heads take FAR longer than data transfers, so you'll slow both operations down a LOT.

 

While the system WILL work, it's definitely best to NOT use the array while it's doing a parity sync or check.

 

If you stop the parity operation and change the configuration (e.g. add another disk), then the parity sync will restart (from the beginning) when you Start the array (or if you're doing a check you'll need to restart it and it will also start from the beginning).

 

... Actually was surprised with the parity check because both disks are precleared.

 

Pre-clearing prepares a disk so it can be added to a parity-protected array without the need to do a new parity sync.  It writes zeroes to the entire disk except for a "signature" area, which identifies it as being pre-cleared.    UnRAID recognizes this, and can simply clear the signature sector and then adding the disk doesn't require any updates to the parity disk.

 

Pre-clearing a parity disk makes NO difference, since the initial parity sync much be done for the entire array regardless of the contents of the disks.  [in fact, if you add disks BEFORE you have done a parity sync, it makes no difference if they're pre-cleared or not, as there's no need for them to be cleared.]

 

Indeed it's a parity sync, not a parity check.

Stopped the data copy, thanks

 

As for preclearing before parity sync: If a parity disk and all the data disks are precleared before starting the array for the first time,

parity sync make no sense to me since all disks have zeroes, so parity sync seems unnecessary.

As for preclearing before parity sync: If a parity disk and all the data disks are precleared before starting the array for the first time,

parity sync make no sense to me since all disks have zeroes, so parity sync seems unnecessary.

 

If you had checked the "parity is already valid" box before starting the array for the first time a parity sync would be unnecessary.

I thought of that, but than it might leave the preclear signature intact, which would invalidate the parity.

I thought of that, but than it might leave the preclear signature intact, which would invalidate the parity.

No, the signature is removed when it's added to the array.

Haven't actually tried that, but I don't think it would work.

 

The pre-clear signature is removed when a drive is added to a parity-protected array.    In the case of two drives being assigned to a new configuration (where there's no existing parity), checking the "parity is valid" box implies parity IS in fact already valid -- which would not be the case with two newly pre-cleared drives [it would be CLOSE to valid, but not in the area of the pre-clear signatures].

 

You could, of course, simply check the "parity is valid" box and then just run a correcting parity check, which would "fix" the few areas where there a discrepancy.    But this would take as long as a parity sync, so there's no advantage of doing so.

 

As I noted earlier, the pre-clear process was designed purely to eliminate the need for UnRAID to clear a drive being added to a protected array.    It's also used a lot to test new drives being putting them in service, but it's NOT designed to eliminate the need for an initial parity sync.

 

Haven't actually tried that, but I don't think it would work.

 

It works, I've used it many times on my test server.

Removing the preclear signature probably writes zeros,

and thus in fact makes the parity valid.

Thank you all, learned something new. 83748379040 to go...

Haven't actually tried that, but I don't think it would work.

 

It works, I've used it many times on my test server.

 

Good to know.  I'm not surprised you tested it ... I kinda figured that even if you hadn't (yet) you would after I posted that 

 

It's NICE to have a stack of SSDs in a spare server -- lets you easily test a lot of stuff that the rest of us can't do nearly as easily