Upgrading dual parity drives?

[Synaptix]

I have two 6 TB parity drives in my setup and looking to upgrade to two 8 TB drives down the road.

 

Might be a dumb question, but do I need to upgrade both drives simultaneously? Or can I upgrade one to 8TB, and the other later? 

 

My assumption is that both will need to be stopped and replaced at the same time. And the instructions would be to just follow the parity drive replacement guide, but do it for both parity drives (stopping, unassigning, etc.) as opposed to one parity drive in the instructions. 

[JorgeB]

Either way, you can upgrade one at a time or both simultaneously.

[Synaptix]

So one at a time won't break anything? Thanks 

[c3]

One at a time will not break anything. Two at once will be much quicker.

[SSD]

If you do one at a time, you are protected from a single disk failure throughout.

 

Doing them simultaneously means you have no fault tolerance while the two parity disks are being built, but it is quicker.

 

But if you have performed a parity check recently, and all of your smart reports look good - I'd do them together. If you have a weak disk, I would do them one at a time. (Actually, if I had a weak disk I'd be looking to replace it before upsizing parity).

 

You can do a new config and add your current parity disk as another data disk, and rebuild both parities while adding the existing parity as a data disk all in one step.

 

It's not the very safest, but it's what I would do.

[garycase]

I'd do one-at-a-time just to maintain fault tolerance.    Although no matter which way you do it I'd do a parity check BEFORE making any changes to confirm all is well before starting.

 

... and if you DO decide to do both at once, I'd definitely NOT add the old parity disk(s) as data disks at the same time => I'd keep both of those disks untouched AND not use the array for ANYTHING while the parity sync was being done.    That way if something DOES happen you can always do a New Config with the original parity disks and check the "Parity is already valid" box and be back to where you started -- and then recover the failed disk.

 

... but I see no reason to not simply do it one-at-a-time and keep the array fault tolerant throughout the entire process.

 

[SSD]

7 hours ago, garycase said:

I'd do one-at-a-time just to maintain fault tolerance.    Although no matter which way you do it I'd do a parity check BEFORE making any changes to confirm all is well before starting.

 

... and if you DO decide to do both at once, I'd definitely NOT add the old parity disk(s) as data disks at the same time => I'd keep both of those disks untouched AND not use the array for ANYTHING while the parity sync was being done.    That way if something DOES happen you can always do a New Config with the original parity disks and check the "Parity is already valid" box and be back to where you started -- and then recover the failed disk.

 

... but I see no reason to not simply do it one-at-a-time and keep the array fault tolerant throughout the entire process.

 

 

Sorry Gary to tip your sensibilities, but with a little know how, you can actually maintain recoverability with the process I laid out. Study the following process, which was created before dual parity but applies to dual parity as well.

 

I would mention, however, that parity, dual parity and other precautions reduce risk but don't remove it. And there are risks that we must acknowledge - like theft, fire, flood, accident, hardware issues, etc. Small risks but these can render our data - not just one or two drives of it - gone. We each have to have a backup plan that allows us to sleep at night knowing that the server is good but not perfect at protecting our data.

 

I think we tend to grab at easy technical solutions rather than use resources to protect against the most important risk. For example, this user is implementing 8T dual parity. IMO, dual parity protection is designed to protect in a very narrow use case. But taking that 8T drive, filling it with the most valuable data in the array and putting it into a safety deposit box for safe keeping - would THAT be a more effective use of that space? Synaptix may already have a backup strategy, but I'm guessing that many implementing dual parity do not. IMO it is really only when necessary backup is in place that dual parity should be considered. And even then, realizing that it is very unlikely to ever be used.

 

And once that backup IS in place, the extremely small risk of building parity on an array of healthy disks, a 1 day activity - with (IMO) in a similar risk category of fire, accident and theft -  is acceptable. I have been here close to 10 years and cannot ever remember hearing of a user that built parity after a recent successful parity check and having a disk fail in an unrecoverable way. With a way to acceptably recover in the event of calamity - I kind of ignore these extremely unlikely risks.

 

But that's me. I certainly respect anyone taking a more cautious approach.

[garycase]

Agree the risk is small, but I simply see no reason to do ANYTHING that eliminates fault tolerance in the array for an unnecessary reason.   And given that Synaptix already has dual parity, it simply seems prudent to replace them one-at-a-time and maintain fault tolerance.   Agree that with some precautions (as I also noted above -- i.e. retaining the original parity disks and not writing to the array during the parity sync) you can retain a recovery capability even if you do both at once ... but WHY??

 

The extra time to do the 2nd replacement is rather irrelevant -- and the array will be fully fault-tolerant during the entire time that BOTH drives are being replaced.

 

As for protection against other possibilities -- as I'm sure you know I absolutely agree r.e. backups -- I suspect few are backed up as well as I am.   I have a complete backup server that has full backups of all 3 of my other servers AND a complete set of off-line backup disks stored in a fireproof, waterproof, data-rated safe.  But if I was upgrading my parity drives to larger sizes, I'd STILL do them one-at-a-time

 

As for ...

15 minutes ago, bjp999 said:

it is really only when necessary backup is in place that dual parity should be considered.

... I decidedly do NOT agree.    I agree that everyone SHOULD have backups of their data (at least anything they don't want to lose -- and it's arguable why you'd bother to build a fault-tolerant NAS if you don't care enough about your data to not want to lose it).    HOWEVER ... many folks simply do NOT retain backups of much of their data -- and in those cases they should ABSOLUTELY move to dual parity, so they at least minimize the risk of losing their unbacked-up data.

 

I agree, however, that if you have a single-parity system and are debating between creating a complete backup and adding dual parity, you should go for the backups first.   But many folks are not, for whatever reason (cost, space, "irrelevant data", etc.) not willing to backup all of their data -- and in those cases moving to dual parity is absolutely a good idea.

 

[SSD]

27 minutes ago, garycase said:

Agree the risk is small, but I simply see no reason to do ANYTHING that eliminates fault tolerance in the array for an unnecessary reason. 

 

 

Did you read the link I sent? You do not loose fault tolerance if you follow that process. I have followed it a number of times and works great. Takes 2 minutes to enable the recovery, If something were ever to go wrong, you'd have the ability to return to the prior configuration. With dual parity, you would actually maintain both parities and recover from a dual drive failure in the event something went wrong! 

 

28 minutes ago, garycase said:

29 minutes ago, garycase said:

it is really only when necessary backup is in place that dual parity should be considered.

... I decidedly do NOT agree.    I agree that everyone SHOULD have backups of their data (at least anything they don't want to lose -- and it's arguable why you'd bother to build a fault-tolerant NAS if you don't care enough about your data to not want to lose it).    HOWEVER ... many folks simply do NOT retain backups of much of their data -- and in those cases they should ABSOLUTELY move to dual parity, so they at least minimize the risk of losing their unbacked-up data.

 

 

As the backup king I'm somewhat surprised at your perspective here. Certainly "all" is best, but "all critical" is a giant step in the right direction! A disk as big as parity would store all critical for many users.

 

The offsite data backup would protect the user's critical data from most all of the risks including fire, theft, accident, accidental deletion, virus, ransom-ware, etc, etc. I DEFINITELY think this WOULD protect a user's data BETTER than dual parity! (Had to get a few CAPS in there. )

 

Cheers!

[garycase]

7 hours ago, bjp999 said:

You do not loose fault tolerance if you follow that process.

 

Actually, you DO lose fault tolerance -- but you don't lose the ability to restore the system to its original configuration.   Semantics perhaps, but nevertheless there's a difference => with fault tolerance you don't have to restore to a previous configuration if a drive fails.    [Also, although I don't recommend using the array during a parity sync/rebuild, you CAN use it if needed if you do it in a fault-tolerant manner; but NOT if you want to preserve the ability to restore to the previous config, as the process you outlined would require.]

 

I certainly agree a complete set of backups trumps dual parity => my point is simply that many folks will NOT invest in a complete set of backups; and for those folks a 2nd parity drive significantly reduces the likelihood of losing data due to a disk failure (assuming, of course, that when ONE drive fails they immediately replace it ... and don't fall into the trap of "don't need to bother, since the system is still fault tolerant").   Granted, if ONE disk is enough to backup all of the data they care about, they should certainly do it => and in those cases that indeed, as I noted, "trumps dual parity".    But for most folks, I suspect a "complete set of backups" requires a lot more than a single disk.

 

[Synaptix]

Guys, thanks a lot. I appreciate all the help. This community is awesome.