Preclear to clear "current pending sectors"

I have a drive that has some Current Pending Sectors.  I thought I would run a preclear on it.  Just not sure how to go about it.  I have a number of movies on the drive.  I figured I could just copy them to another drive, then unassign the drive, then preclear it, then pop it back in and if the current pending sectors are gone, copy the files back. 

 

Is it as straightforward as that or do I have to run a parity check after unassigning it, then run another parity check after assigning it?  I was hoping I wouldn't have to as it will take quite a bit of time.

Ok, copied all my movies off...now just not sure how to proceed next.

This is what I would do.  I would run at least two preclear cycles on that drives using either JoeL's original preclear script or the plugin GUI interface one.  I would make sure that the pending sectors went to zero after the first cycle which will increase the number of Reallocated Sectors by the same amount.  On the second cycle, the number of pending sectors should remain zero and the Reallocated Sectors remain unchanged.  (Both of these utilities/plugins will provide you with the results after each cycle so you can run a two cycle test and wait until both are completed.)

 

If, on the second, cycle, the pending is not zero and/or the Reallocated Sectors has increased, I would 'deep-six' the drive...  (There are a lot of folks here, that would do that without bothering with the preclear!)

 

Remember that your array will not have parity protection until after you have rebuilt this drive onto either onto itself or a new Drive!

Ok, copied all my movies off...now just not sure how to proceed next.

Assuming you haven't changed your disk assignments in any way you will ultimately rebuild the disk either to itself or a new disk, so the files will be back on the disk anyway.

I'm still a little confused on the process of unassigning the drive the first time.  I stop the array, unassign the drive, then start the array.  Is it going to ask me to start a parity check or a new config...just not sure...then I would start the preclear.  Then when it's done, if it's good, I would assign it back and I guess a rebuild would run even thought there were no files on the drive...

I'm still a little confused on the process of unassigning the drive.  I stop the array, unassign the drive, then start the array.  Is it going to ask me to start a parity check or a new config...just not sure...

It is going to run without the drive, emulating the drive by calculating its contents from parity and all the other disks.

 

When a disk is missing, unassigned, or disabled (red X), unRAID can calculate the disk's data from parity plus all the other disks. This is how it is able to rebuild a disk. And if you try to read the disk unRAID calculates its data in just the same way. And if you try to write to the disk, unRAID will actually update parity as if the disk was written, so it can later read that written data by calculating it in just the same way.

Ok. I did know that but was a little unsure as I've only gone through the process of replacing a drive which was pretty straightforward. 

 

It's going to be a long two days of preclearing...

This is an important task, one that comes up now and then, the problem of what to do with an array disk with pending sectors.  I think we need to come up with a bullet-proof step by step procedure, with clear steps that minimize the risk as much as we possibly can.

 

It would be really nice if we had a tool to deal with them.  I've always wanted to get into Linux programming, enough to produce a little utility that could take a given LBA (or set of LBA's) and rewrite it as safely as possible, SpinRite style, restoring the original contents while preserving parity protection.  But I'm much better at ideas than accomplishments, can't stay on track.   

... and I guess a rebuild would run even thought there were no files on the drive...

An empty filesystem is not a clear disk. The filesystem itself is data stored on the disk. The clear disk will not be consistent with parity, so the disk will have to be rebuilt or parity will. Both are basically the same activity but rebuilding parity would require you to do a little more in the webUI, so might as well rebuild the data disk.

Personally, I'd prefer to rebuild onto a new, tested disk as soon as possible and then investigate the old one at my leisure. If it turns out to be usable then fine, I can label it and put it back on the shelf. If it turns out to be bad then I've wasted a lot of time and my array will have been degraded for several days.

Personally I think the whole idea of:

 

1) - empty the drive

2) - unassign drive

3) - run preclear on unassigned drive

4) - if drive ok: assign drive to unassigned slot and rebuild on itself

 

is a bit weird... During this whole cycle (and with big drives that can be several days) you are running without (or with limited if you have two parity drives) parity protection..

 

Another option would be:

 

1) empty the drive

2) unassign drive

3) redo parity and in parallel start the preclear

4) if drive is ok add to array and redo parity again

 

Problem with that one is that you have two times you are running without parity (or reduced), so thats not ok either..

 

The best option remains to make sure you have precleared disks on standby that can be used as replacement disks immediately, and then do your preclears and tests on the old drives at your leasure.. This however works best if you have all the same size disks in your array (because your spare disk would need to be the biggest disk and the disk that you might "salvage" after the preclears could not be lower (or at least if it is not as big you cannot use it as your new "spare disk"...

 

Having all the same sized disks goes against the advantages of unraid against competitors..

 

So there is no real golden solution me thinks..

 

(and yes: ofcourse you need backups to avoid data loss, I have all my data backupped on a second system, but I am not looking forward to using them ;-)

Personally, if I were in one of these situations, I would shut down and wait on Amazon Prime. That way I can get a replacement disk of the size I want and at current prices, which are likely lower than at some earlier date.

Personally, if I were in one of these situations, I would shut down and wait on Amazon Prime. That way I can get a replacement disk of the size I want and at current prices, which are likely lower than at some earlier date.

 

You could... But you would need to keep your array off for a week and do your preclears on another system ?

Personally I think the whole idea of:

 

1) - empty the drive

2) - unassign drive

3) - run preclear on unassigned drive

4) - if drive ok: assign drive to unassigned slot and rebuild on itself

 

is a bit weird... During this whole cycle (and with big drives that can be several days) you are running without (or with limited if you have two parity drives) parity protection..

 

Another option would be:

 

1) empty the drive

2) unassign drive

3) redo parity and in parallel start the preclear

4) if drive is ok add to array and redo parity again

 

Problem with that one is that you have two times you are running without parity (or reduced), so thats not ok either..

 

 

We posted near simultaneously and I agree. In the first case though, step 1 is unnecessary and in the second case, redoing parity in step 4 is unnecessary.

 

Perhaps an answer is triple parity. Since the hard work has already been done to introduce dual parity, I'd like to see it as an option.

 

Personally, if I were in one of these situations, I would shut down and wait on Amazon Prime. That way I can get a replacement disk of the size I want and at current prices, which are likely lower than at some earlier date.

You could... But you would need to keep your array off for a week and do your preclears on another system ?

Supposed to be 2-day delivery though it sometimes slips a bit. Right now we are having snow delays, but I wouldn't expect it to be a week even now. And my backup server is ready and waiting. That is where I do preclears now.

 

Personally I think the whole idea of:

 

1) - empty the drive

2) - unassign drive

3) - run preclear on unassigned drive

4) - if drive ok: assign drive to unassigned slot and rebuild on itself

 

is a bit weird... During this whole cycle (and with big drives that can be several days) you are running without (or with limited if you have two parity drives) parity protection..

 

Another option would be:

 

1) empty the drive

2) unassign drive

3) redo parity and in parallel start the preclear

4) if drive is ok add to array and redo parity again

 

Problem with that one is that you have two times you are running without parity (or reduced), so thats not ok either..

 

 

We posted near simultaneously and I agree. In the first case though, step 1 is unnecessary and in the second case, redoing parity in step 4 is unnecessary.

 

Perhaps an answer is triple parity. Since the hard work has already been done to introduce dual parity, I'd like to see it as an option.

Don't see why triple parity would be necessary, unless you insist on still having double protection while you have only one missing disk.

Personally, if I were in one of these situations, I would shut down and wait on Amazon Prime. That way I can get a replacement disk of the size I want and at current prices, which are likely lower than at some earlier date.

You could... But you would need to keep your array off for a week and do your preclears on another system ?

Supposed to be 2-day delivery though it sometimes slips a bit. Right now we are having snow delays, but I wouldn't expect it to be a week even now. And my backup server is ready and waiting. That is where I do preclears now.

 

Gottit... For me that would not work... A thorough preclear takes me at least 3 days, with those two days delivery I would still be facing five days without a server, I couldn't cope ;-)

Personally I think the whole idea of:

 

1) - empty the drive

2) - unassign drive

3) - run preclear on unassigned drive

4) - if drive ok: assign drive to unassigned slot and rebuild on itself

 

is a bit weird... During this whole cycle (and with big drives that can be several days) you are running without (or with limited if you have two parity drives) parity protection..

 

Another option would be:

 

1) empty the drive

2) unassign drive

3) redo parity and in parallel start the preclear

4) if drive is ok add to array and redo parity again

 

Problem with that one is that you have two times you are running without parity (or reduced), so thats not ok either..

 

 

We posted near simultaneously and I agree. In the first case though, step 1 is unnecessary and in the second case, redoing parity in step 4 is unnecessary.

 

Perhaps an answer is triple parity. Since the hard work has already been done to introduce dual parity, I'd like to see it as an option.

 

If you do tripple parity you still run the same risk down the road, so then you want quad-parity.. I do not think that is the way to go..

 

Ehm.. emptying the drive is not useless... Suppose you have 2 parity disks and you have a dual drive failure, then suppose you get another fail.. Then parity no longer works and you loose 3 drives.. If one of those drives was emptied before you have still lost the contents of that drive but the contents were empty...

 

Bit of a fringe case, I agree, but valid..

And if a disk's contents are lost, of course you have backups if those files were important.

To be honest, I was trying to avoid buying another drive at the moment. I'm going from a larger 10drive system to a smaller 4 drive system.  I already bought the Lian Li Q25.  I deleted a ton of movies, just trying to keep my favs.  Plus a few other items. 

 

I'm not to worried about being without parity for a little while as I'm not using my server at all until all this is done.

One other question.  With new drives, do I need to worry about jumper settings for 4k aligned or do I just leave them off totally and use the Webgui for 4K aligned?  As far as I recall, my last drive I just left the jumpers off and just used the Webgui to set the 4K alignment but not 100% sure anymore as it was more than a year ago.

One other question.  With new drives, do I need to worry about jumper settings for 4k aligned or do I just leave them off totally and use the Webgui for 4K aligned?  As far as I recall, my last drive I just left the jumpers off and just used the Webgui to set the 4K alignment but not 100% sure anymore as it was more than a year ago.

It's been years since I have had any concern about that. What size drives are you talking about?

2TB or 4TB...I'm pretty sure I didn't worry about jumpers on my last drive but just wanted to double check.  Just running a preclear on a disk now.  I probably have to do so on 3 other drives as well.  I may just end up buying one or two 4TB drives.

Yikes!  I was just copying files to my disk 3 and when I went to the main page to unassign my disk 10 to run preclear, I see my disk 3 has a red x next to it and is offline.  Not sure what to do now.  I've been looking around the guides for what to do when you see a red x but can't find anything.

tower-diagnostics-20170107-1633.zip

and here's the syslog...large red sections in this one...Heading out now to buy a 4TB Hitachi...

tower-syslog-20170107-1636.zip