I just ordered 3-3TB drives, and would like recommendations on upgrading my system.  My current system:  3TB cache, 2TB hot spare/cache, array of 1.5, 1.5, 2, and 2 TB drives. One of the 2TB drives appears to be failing, so it has to be replaced.  I have another 2TB drive that used to be the parity drive I could use for replacement.  I just upgraded to version 6.2.4 (upgrade went smoothly, though I did have to do a hard power down).  All the data drives are well over 90% full.  My system will support the addition of one more drive.  I back up all my critical data to two different 4TB drives, one of which I keep offsite.

 

If I want to keep a hot spare/cache, do I make this a 3TB drive?  That makes the most sense to me, but maybe I don't have to do this. 

 

I could replace the 2-1.5 TB drives with 2-3 TB drives, and the failing 2TB with another 2TB.  This also seems to make the most sense.

 

However, should I consider the new 2nd parity option, especially since I can add one more drive?  Or is the second parity drive even useful with only four data drives?

 

And when I go about doing this, I remember there's a way to test/burn in and configure a new drive.  After that, I take out a data drive and rebuild the parity.  Do I keep the system running a while after that, say a week or so?  Or once the parity is good, do I set about burning in a new drive and replacing another drive immediately?

 

Also, I have a USB drive case I could use to help burn in and test the new drives.  That is, it's a case with its own power supply that supports large drives and communicates via USB with the computer.  I use these cases for my portable backups.  Does unraid support these types of cases?

If you want an opinion regarding which drives are most in need of replacement post your diagnostics.

 

You don't actually mention the size of your current parity drive. Of course it will need to be at least 3TB if you are going to have 3TB data drives.

 

It has been reported that some USB enclosures don't report SMART which you will want when testing the new drives so it might be easier if you have the spare ports to just use SATA.

 

As for whether dual parity is worthwhile with a small number of data disks it is a tradeoff I debated for a while. Do I want to use my limited disk bays/ports for another parity or another data disk? I ultimately went with dual parity just so I would have experience with that feature.

A few random thoughts ...

 

=>  r.e. the order to replace the drives.    You indicated you have a 2TB drive that "appears to be failing".  Not sure how you came to this conclusion, but nevertheless the FIRST thing I'd do, since you have a spare 2TB drive, is replace that drive and let it rebuild.  You do NOT want to have a drive fail in the middle of replacing your parity drive (which I presume you need to upgrade to 3TB -- is that correct?  ... or is it already a 3TB drive?).

 

=>  One key point:  I presume you have run a current parity check and know that parity is good (i.e. there were no sync errors).  If not, that is the FIRST thing you should do -- BEFORE the drive replacement I just noted.

 

=>  r.e. dual parity.  Up to you whether you want to add this additional layer of fault tolerance.  It very significantly improves the fault tolerance of your system, since if a drive fails you can do a rebuild of that drive and even if another drive fails during the rebuild it will still successfully finish.    But it does, of course, "cost" a 2nd dedicated parity drive; and a possibly valuable drive slot.    With only 4 data drives, and a complete set of current backups, it's not all that much of a risk to run with single parity.    Personally, I use dual parity on all but one of my v6 servers -- and the only reason I don't use it on that one is I'm out of both SATA ports and drive slots.

 

=>  r.e. testing your new drives.  You can do this on a PC using WD's excellent Data Lifeguard.  This will run fine on a USB connected drive, although it's notably faster if you connect directly to a SATA port.  Or you could use the pre-clear utility in UnRAID to test them on UnRAID, although you don't actually need to clear the drives, so you'd only be using that as a testing utility in this case.    Depends primarily on just what systems you have available to do some testing on.

 

=>  Summary:  Assuming you do not currently have a 3TB parity drive; the basic process is (a) test the new drives; (b) be sure you've done a current parity check;  © replace the failing 2TB drive before starting anything else; (d) upgrade to a 3TB parity drive; and finally (e) replace your smallest drives with the other 3TB drives  [Or replace one of them, and use the last 3TB to upgrade to dual parity].

 

Thank you.  Sorry, I do have a 3TB parity drive. 

 

The reason I say a 2TB drive may be failing is the attributes for that disk lists a reallocated sector count of 200, which is over the threshold of 140.  However, the "SMART overall-health" is "passed", and that sector count has remained the same for a long, long time.  So, I'm not totally sure if the drive is failing, but there is a warning for this drive on the "SMART status" of the dashboard.  I figured since I'll be messing with the system and I have two extra 2 TB drives, I might as well replace the drive that might be failing too.

 

I just did a parity check that was fine.

After reading the replies, I'll burn in/test the drives (maybe using both windows and unraid), run another parity check, then replace drives starting with the 2TB, and replacing at least the two 1.5TB drives with 3TB.  For the 2 TB drive that might be failing, I'll probably replace that with a 2TB.  I'll have to make a decision as to the third 3TB--keep as cache and hot spare, or use as second parity.  I'm leaning toward using as a cache/hot spare.  Otherwise, I'd need to get another 3TB drive, since I think a hot spare is a wise idea.

 

Hmmm...3TB WD blue drives went up in price today on Amazon, even though it's Black Friday.

Note that the reallocated sector count isn't something I'd worry about as long as the number is essentially static.

 

Modern drives are DESIGNED to automatically reallocate sectors that it detects are unreliable.  The parameter you do NOT want to be non-zero is "pending sectors" => these are sectors the drive has determined are unreliable, but has not been able to reallocate them because they contain data it's not been able to successfully read (and thus can't reallocate the sector).

 

I wouldn't necessarily replace that drive if that's the only parameter that's concerning you.

 

I wish you had posted up about your choices earlier before you ordered the drives.  I would have suggested that you consider looking more carefully at selecting any even larger parity by looking at the cost /per TB when you are adding more space to your array.  For example when you are using a 3TB drive to replace a 2TB, you only get one TB of increased space.  Now calculate the cost of that 1Tb!  Now consider replacing that same 2TB with a 6TB drive(~2X the cost)  but you get 4TB of additional store space.  Now calculate the cost per TB for that space.

 

These type of decisions are difficult to make at the time but always be thinking about the future.  If you went with the 6Tb size (for example) you would save the purchase of three additional 3TB drives to gain that same 4Tb of extra storage!)  The biggest issue is that you have to commit to that 6Tb parity drive purchase now to be in a position to save the money further down the road. 

I wish you had posted up about your choices earlier before you ordered the drives.  I would have suggested that you consider looking more carefully at selecting any even larger parity by looking at the cost /per TB when you are adding more space to your array.  For example when you are using a 3TB drive to replace a 2TB, you only get one TB of increased space.  Now calculate the cost of that 1Tb!  Now consider replacing that same 2TB with a 6TB drive(~2X the cost)  but you get 4TB of additional store space.  Now calculate the cost per TB for that space.

 

These type of decisions are difficult to make at the time but always be thinking about the future.  If you went with the 6Tb size (for example) you would save the purchase of three additional 3TB drives to gain that same 4Tb of extra storage!)  The biggest issue is that you have to commit to that 6Tb parity drive purchase now to be in a position to save the money further down the road.

 

Those are very good points.  In fact, I saw that Newegg had some 4TB drives on sale on black Friday for not too much more (I think $20 each) than what I paid for my 3TB.  My unraid server and electronics infrastructure get shorted by me, because I have a desk job in front of a computer and the last thing I want to do on the weekend is sit in front of a computer.  It's only because I've had shoulder surgery -- and can't do anything else -- that I'm getting around to upgrading the unraid server.  So, I'm used to making rash decisions because I typically have such little time.

 

The engineer in me wonders about adding in a drive that's much larger than the other drives and the effect on parity.  For instance, if I added in a 6TB drive to replace a 1.5 TB drive (and add a 6TB drive for parity), then I'd have 6, 1.5, 2, 2 TB data drives.  Is that as good as 3, 3, 2, 2 TB?  For some reason, the latter seems better to me for a parity calculation (you have at least three drives instead of two), but I don't know how parity is calculated in unraid.

 

Also, we have about 3+ TB of our own data, which is not growing that fast.  The rest of the space is recorded TV, which I do not back up.  In fact, if I deleted some of the 50+ Antiques Roadshows and shows the kids no longer watch, I could extend the life of the array in terms of size.  So, I was thinking of adding a bit more space instead of a lot.  But I could've added much more space and not have had to think about the array for a longer while.

 

I do think I'm going with double parity, if I can.

If you have 1 parity and 1 data drive unRAID creates a mirror of the data from disk1 to parity1.

If you have 1 parity and 1 data drive unRAID creates a mirror of the data from disk1 to parity1.

That is effectively what happens but the single parity calculation is the same regardless of how many data drives you have.

... I don't know how parity is calculated in unraid...

See this wiki article. Many things about using unRAID make more sense if you know how unRAID calculates and uses parity.

...  I don't know how parity is calculated in unraid.

 

The first parity disk uses a simple longitudinal even parity calculation => just XOR's all the bits in any given bit position across all drives and forces the end result to be a zero (thus "even" parity).  The Wiki has a more detailed discussion of this, but if you understand basic parity calculations, it's very simple.

 

So the SIZE of the parity disk is completely irrelevant in terms of how much "protection" you get => the only constraint is it must be at least as large as any of the data disks (else there wouldn't be a parity bit available to protect some of the data).    So if all your disks are 1.5TB, then a 1.5TB parity disk provides exactly the same protection a 6TB parity disk would ... the extra 4.5TB of space on the parity disk would effectively be unused [it would actually still be "checked" and set to the appropriate parity to protect itself].  Your parity checks would, however take a good bit longer, since a parity check will check the complete size of the parity disk.

 

What a larger parity disk does is provides you with the ability to use data disks of that size.  So if you had a 6TB parity disk and one of your 1.5TB disks failed (or you just wanted to upgrade it to a larger size), you could replace it with a 6TB data drive.

 

In other words, it doesn't make sense to use a larger parity disk than the largest data drive you plan to use => but be careful when deciding what that might be, as data needs have a way of growing much larger than you might have expected 

 

... forgot to add:

 

The second parity disk, if you upgrade to v6.2 and decide to use dual parity, uses a more complex parity calculation but the basic rule is still the same:  i.e. it has to be as large as the largest data disk.  So if you DO decide to go with a dual parity setup, simply use two parity disks of the same size.

 

Thank you.  It's a bummer that I didn't post before buying drives, but I'll know better next time.

With either 3 or 4 data drives in your array, you might want to read this thread about deciding whether dual parity is going to buy you that much.

 

      http://lime-technology.com/forum/index.php?topic=52229.msg501203

 

 

With either 3 or 4 data drives in your array, you might want to read this thread about deciding whether dual parity is going to buy you that much.

 

      http://lime-technology.com/forum/index.php?topic=52229.msg501203

 

Nice information, Frank.  after thinking about this, in the many years I've had my server going, I think I've only replaced at most two drives -- it may have only been one -- due to drive failure.  I usually have to make the array bigger and replace drives because of that. I've also had hardware failures, which are much worse,  and more time consuming to recover from.

 

That gives me more to think about.

Just don't beat yourself up over buying drives.

 

I'm just recently buying 3TB and 4TB drives because lets face it we are not all made of money and sometimes you buy things based on need vs want.

I bought a couple 3TB's for Data Drives for $88 each and a 4TB Parity drive for just over $100. Sure I could of gotten more TB for a bit more, but sometimes its easier to sell a lower number to the miss's than hey if I buy this 6TB I can get it at a lower price point when all she see's is 2X the money I was dropping not 2X the space. lol

 

I purposely built my machine with available physical space so I can swap in/out new drives as I juggle the need for more space. Heck I have a couple of 500gig drives living in my machine right now. Sure they are older, but have great smart reports and low hours and rarely get spun up except for home video/photo back up now and then and a parity check.

Agree r.e. a bit of conservatism on drive sizes.

 

I see a lot of folks buying 6TB (or even 8TB) parity drives with an array full of 1, 1.5, and 2TB drives.  This is, IMHO, a waste.  If the array is providing the storage you need; and you want the ability to expand a bit, moving to perhaps a 4TB parity drive would seem to make more sense.  ... you'll ultimately be able to better than double the storage capacity in the system with 4TB drives, and won't have one (or two, if you choose to use dual parity -- a good idea, but not something everyone will do), 6TB drives invested in providing fault tolerance for drives 1/3rd that size (or smaller).

 

On the other hand, if you've suddenly changed your usage scenario from an occasional collector of music CD's to an avid ripper of BluRay disks, then you may need to start moving rapidly to the much larger drives -- and if that's your plan, then of course you should get a parity drive that will support the size drives you plan to buy.

 

In other words -- you need to THINK about how your server needs to grow; and be sure any increase in the size of your parity drive reflects what you are realistically going to buy in terms of drive sizes.

 

r.e. the "effective cost per TB" of a new drive, where you compute the cost purely based on how many TB you're adding.  This is, of course, a valid argument -- BUT there are two other things to consider:  (a)  If you primarily just replace drive when they fail; then it's irrelevant -- you're adding the total capacity of a new drive when you do the replacement, since you need to buy a new drive anyway;  and (b)  using a larger parity drive (or drives) also means you're investing a higher cost in providing fault tolerance, since you have to buy one (or two) of that size drive to provide that feature.

 

e.g. using Franks's earlier example of moving to a 3TB parity and upgrading 2TB drives.

 

(a)  If you simply bought the 3TB parity; then replaced 4 2TB drives with 3TB drives; it would indeed be rather expensive compared to using 6TB drives.  You could, as Frank noted, use a 6TB parity and replace one of the 2TB drives with a 6TB drive and achieve the same 4TB of increased space in your array.    It's not as bad as it sounds, however, when you look at the actual costs.  Using today's Amazon prices, 5 3TB WD Reds would cost $545 ($109 ea); whereas a pair of 6TB Reds would cost $462 ($231 ea).  So yes, if that was what you were doing, it would cost $83 more to do that upgrade.  However, if you were also moving to dual parity, the economics of that would be different -- you'd need 6 3TB drives ($654) or 3 6TB drives ($693) to do the same thing.

 

(b)  If you were just upgrading parity to prepare yourself for future capacity growth, then you'd either be spending $109 for a 3TB drive (or $218 if you want dual parity) or $231 for a 6TB drive (or $462 if dual parity) -- and gaining NO space at this point.  Then, when you needed additional capacity, or if a drive failed, you'd be buying additional drives.  Note, however, that if a drive fails, the replacement drive you're buying is effectively providing ALL of its capacity to the array, since the failed drive is no longer usable.

 

Don't misread my point => I DO think it makes sense to buy as large a parity drive as you think you might reasonably need.  But be sure you THINK about what is really reasonable for your particular situation.    The question I'd ask yourself is:  If I buy an X TB parity drive, am I going to buy X TB data drives from now on?  If the answer is no, then X is probably too large a value 

 

Yep what Gary said. Lol

 

I need to get Garys Phone number and hand the misses the phone with him on it when I'm arguing prices on stuff when I want to buy them. She'll either say. "Fine he has a good point" or slap me for ganging up on her. 

Yep what Gary said. Lol

 

I need to get Garys Phone number and hand the misses the phone with him on it when I'm arguing prices on stuff when I want to buy them. She'll either say. "Fine he has a good point" or slap me for ganging up on her. 

 

I'll pass on discussing YOUR purchases with YOUR wife 

 

I actually agree with your comment that you should "...  buy things based on need vs want ..." ==> within reason.  But if it's clear that your FUTURE needs are clearly going to require significant storage increases, then it makes sense to buy a parity drive that will support those; and not put yourself in a situation where you have to upgrade your parity drive multiple times.    On the other hand, as I also noted, it makes no sense to buy, for example, a 6TB parity drive unless you are only going to buy 6TB data drives in the future.  Buying a 6TB parity drive; and then adding 3TB or 4TB data drives to your array, simply doesn't make sense.

 

Fortunately my spouse doesn't give a rip what I spend on my hobby 

 

One minor point is that BackBlaze's drive failure data doesn't seem to indicate that larger drives have a inherently  greater failure rate than smaller drives.  So , it is likely that two arrays with the same storage capacity, the one with fewer drives will be more reliable.

 

      https://www.backblaze.com/blog/hard-drive-reliability-stats-q1-2016/ 

 

If you know that future planning indicates that you will require twice as much storage as you presently have within the next eighteen months, your strategy should be different than if it was going to take five years to double your requirement. The 'sweet spot' for hard drives has always been a moving target.

 

I can remember when I bought my first hard drive, it was a 10MB one (cost ~ $500) and I thought I would never be able to fill it up...

... I can remember when I bought my first hard drive, it was a 10MB one (cost ~ $500) and I thought I would never be able to fill it up...

 

My first hard drive was a 14" Seagate 26MB unit for my CompuPro CP/M system -- after a 10% discount it cost me $4500.  And yes, I too thought it was an amazing amount of storage that would take a long time to fill up !! 

... and I now carry a 128GB USB flash drive in my pocket (on my key ring) => that's 4,923 times as much storage as that first hard drive had; and it cost me about 1/100th as much 

I worked at Honeywell, and when I got there they still had 40 M B drives that were as big as washing machines. Also, I remember my first 40 MB drive for my computer was expensive, massive, and took forever to spin up.

 

I remember now that there's only been one drive I have had to replace to failure, at least that I can remember. And I've had my current system for longer than I can remember. I think I started out on version 4, and ran that for years.

 

I believe what I will do is the following:

 

3TB parity (current, leave alone)

 

Data drives:

replace 1.5 TB with 3TB

replace 1.5TB with 3TB

2TB (current, leave alone)

2TB (current, leave alone)

Convert 2TB cache/hot spare to 2 TB data drive (expand array -- I'll do this last, as it takes up my last drive slot)

 

Cache/hot spare: Change current 2TB drive to 3TB cache/hot spare

 

I am still not totally sure about expanding the array, as I will lose my last drive slot, and for now I do not need the extra two TB. If I lose my last drive slot, then I will not be able to pre-clear new drives by using the array/server. I would have to use a Windows computer and probably a USB box. I also have an extra 2TB drive, previously used and sitting near the array, which I can use should a 2TB drive fail.