I have recently picked up a couple of 6TB drives that I want to put into use as my array is getting tight on space. I have already replaced my older 4TB parity drive with one of the 6TB drives. So I have another 6TB and the old Parity to put into the array. Most of my other drives are 2TB. I am trying to figure out which ones to upgrade. None are showing any overt signs of failure. SMART reports are showing some warnings by using MyMain and unmenu, but as I read it these are not really operationally problematic, see here:

 

Seagate drives showing high load cycle count values - this seems to be an issue with the head parking routine on these drives.

A few drives showing some high fly writes, but not increasing.

A Samsung drive showing a multi zone error rate that is not changing.

A Hitachi drive that shows an ATA error, but that was when it was first added many moons ago and not recurring

 

So assuming that my assessment of these errors is that they are not immediately indicative of a bad drive, what is the most useful criteria to pick out which drive to replace? Just Power on hours so I get rid of the oldest drives first, or should I look for something else?

 

Thanks for any light that can be shed.

All else being equal, I would replace the drive with more critical data on it first. Or at least move the data around first so all old drives contain noncritical data.

I have had the same issue many times, and I always just replace the oldest drive. 

I'd go by oldest/smallest, best way to hedge your bets.

Replace smallest, as you will gain the most from your purchase.

 

Drive age is not a good predictor of failure. But your smallest are likely to be the older, if not oldest drives.

Thanks for the replies. I was planning on going FIFO unless the errors from the OP are more concerning to anyone. There are a bunch of 2TB ones so going by size won't help right now, but would have been my first criteria.

Would also just replace the oldest.  Maybe the oldest Samsung / Seagate.

Yes, that one Samsung is probably on the chopping block. 

You are right that none of the issues you found are particularly concerning.

 

I would replace the smallest one - normally also the oldest one.

 

If selecting from a group of 2T drives I would choose by brand, I would axe the Samsung first, then the Seagates, then the WDs, and keep the Hitachi/HGSTs the longest.