Parity Check & Preclear Protocol - Replacing Old (Now Empty) Drive Currently In

[wheel]

Quick question:

 

It's been about a month since I've run a parity check (which came back fine), and I'm about to replace an old drive in my array with a larger new drive (no slots left, it was only 1TB, and I've moved all its content to other drives in the array).

 

Should I run my monthly parity check BEFORE or AFTER I remove the 1TB from the array (bringing it down to 18 drives so I can safely run preclear on my new drive while the array is running)?  Or (and I'm pretty sure the answer is "no," but I figured I'd ask) am I better off simply killing the array for a few days' preclear and then "reconstructing" the empty drive as a way to give all of my drives their monthly workout?

 

Thanks in advance for any guidance you can provide!

[garycase]

Before making any changes to the array I'd run a parity check.

 

As for pre-clearing the new drive -- do you have a spare PC you can do that on?

 

You can use a different USB Flash drive -- just install the basic UnRAID download on it along with the pre-clear script ... no need for a key, the free version will work fine.

 

Then you can replace your 1TB drive and let the system rebuild it on the new drive.

 

[garycase]

... just re-read your post and noted that the 1TB drive is empty (no content).

 

In that case, if you don't want to pre-clear on a different machine, I'd do the following:

 

(a)  Run a parity check to confirm all is well.

 

(b)  Create a "New Config" with the 17 drives you want to leave in the array => Be SURE you know which drive is the parity drive, so you assign it correctly.    Simply leave the old 1TB drive out of that config.

 

©  Start the new array and let it do a parity sync.    When that finishes, run a parity check to confirm all went well.

 

(d)  NOW install the new drive in the system, and run a pre-clear on it.    Note you can use your array during this process, as the pre-clear is completely "outside" of the active UnRAID system.

 

(e)  When the pre-clear finishes, Stop your array and add the new drive -- this will be very quick (it just needs to format the new drive when you start it back up).

 

Note, however, that the process outlined in my first post (using a different PC for the pre-clear) doesn't require any "at risk" time for the array.  The process outlined in this post results in running "at risk" until the new parity sync operation is completed.

 

[itimpi]

Just a note - once the 'new config' has been done in step (b) you might as well put the new drive in and start the pre-clear step (d) in parallel with ©.  Step © rewrites the parity so the old 1TB is no longer relevant.  Running © and (d) in parallel will reduce the total elapsed time before you are ready for (e).

[wheel]

No spare PCs, unfortunately (just a couple of laptops, none with eSATA), so I'm probably going to shoot for itimpi's hybrid suggestion that seems to maintain array protection the whole time - one parity check now, then set up the 'new config' with 18 drives instead of 19, then initiate preclear while 'new config' is calculating new parity.

 

In this case, does it make more sense for me to save my final parity check for AFTER the new 19th drive has been pre-cleared and added to the 'new config' 18-drive setup?  Or should I still run another parity check immediately after the parity sync for the 'new config,' prior to adding the new 19th drive?

 

Thank you both for all of your help!

[Joe L.]

In this case, does it make more sense for me to save my final parity check for AFTER the new 19th drive has been pre-cleared and added to the 'new config' 18-drive setup? 

That would work, and save a bit of time.

[garycase]

... that seems to maintain array protection the whole time - one parity check now, then set up the 'new config' with 18 drives instead of 19

 

No, it does NOT "maintain array protection".  You're running "at risk" the instant you create the New Config.    From that point until the initial parity sync is completed (many hours) there is no protection on the array.

 

 

... initiate preclear while 'new config' is calculating new parity.

That works fine, and does indeed save some time, since they're both working at the same time.

 

 

 

 

[itimpi]

In this case, does it make more sense for me to save my final parity check for AFTER the new 19th drive has been pre-cleared and added to the 'new config' 18-drive setup?  Or should I still run another parity check immediately after the parity sync for the 'new config,' prior to adding the new 19th drive?

Not really necessary to wait.  Adding a pre-cleared disk to an array does not invalidate parity.

[garycase]

In this case, does it make more sense for me to save my final parity check for AFTER the new 19th drive has been pre-cleared and added to the 'new config' 18-drive setup?  Or should I still run another parity check immediately after the parity sync for the 'new config,' prior to adding the new 19th drive?

Not really necessary to wait.  Adding a pre-cleared disk to an array does not invalidate parity.

 

Adding a pre-cleared disk to an array does not invalidate parity;  but doing a New Config does.

 

[wheel]

Ahh, that makes sense - so by running my pre-clear before I try the 'new config,' I'm minimizing the chances of a dead disk (or even worse, two-plus) during the new parity sync (which will probably take 12-16hrs with the existing 4TB parity disk and all the 3-4TBs in this tower).

 

Do you recommend any additional preclear flags or unmenu tricks that could help a little extra towards ensuring my unprotected 'new config' period is as safe as it can possibly be?

[wheel]

Forgot to mention (in case it matters or an update is highly recommended before proceeding):

 

Running 5.0-rc6-r8168-test

[itimpi]

The pre-clear is not relevant to minimising unprotected time.  You need to create the new parity as soon as you have done the 'new config' to remove the 1TB drive to minimise the unprotected time.

 

If you really want to never be unprotected then you need to do whatever pre-use testing you want to do on the new drive (normally done via pre-clear), and then following the process for replacing a drive by a larger one.  However this takes significantly longer elapsed time.

[garycase]

As I noted much earlier, the only way to never have to run "at risk" is to simply replace your 1TB drive with a new drive.  You can either pre-clear this drive on another system;  or simply take a chance and add it without pre-clearing it.

 

Anything else results in some "at risk" time.  [The time to do a parity sync with a new configuration]

 

[wheel]

I think that's the part that's killing me - I've been through dozens of drives with no issues ever arising on preclear, and then out of the blue, my last new drive actually died mid-preclear (cycle 1 out of 2).  Had that not happened, I'd probably just have slapped the new one in over the 1TB... Now, especially with a not-so-cheap 4TB in play, I feel like I really need to preclear.

 

I guess I'm just going to bite the bullet and try the 'new config' option after I run a normal parity check tomorrow, and just try and do it on a day when I know I'll be occupied by something that'll keep me from going back and checking the parity sync every few minutes

 

Thank you again for all of the assistance!

[garycase]

Agree it's a good idea to pre-clear the drive to get a bit of confidence in it.

 

The best choice would have been to do the pre-clear on a different PC, so you could then replace the 1TB with a pre-cleared drive and never have to run "at risk."

 

But in the absence of that; a parity check (to confirm all's okay); followed by a New Config to free up a slot; will at least minimize the "at risk" time to the time it takes to rebuild parity.  Note that after the parity sync finishes, you should run a parity check to confirm all went well.

 

Meanwhile, you can be pre-clearing the new 4TB drive .. and when it's done, you can add it without impacting the parity protection on the array.

 

[dgaschk]

Before any config changes run a parity check and make a backup of the flash drive. After the change and the array is functioning run a parity check. The answer to the parity check question is both. Do one before and one after the modification. And don't forget to backup the flash drive!

[wheel]

Thank you again for the advice, everyone - the "new config" is protected (parity check before and after new sync), and the new drive is working its way through two preclear cycles.

 

Next step: upgrading to 5.0 final!