RAID Migration or Clean Install

Well every time I buy bigger drives I say “I’ll never run out of space now”. NOT!

My NAS is a QNAP but I’m curious as as general rule is it better to start from scratch with a clean install when changing from Raid 1 to Raid 5? Or does it not matter.

I’ve got a 4 bay NAS with two 10 TB drives configured for RAID 1, and two bays empty. I’m planning on adding two more 10TB drives and going with Raid 5 for a total of 30TBs for movies, pictures and of course music.

I don’t want to run into problems down the road, but it will literally take days to restore all my backups if I start with a clean Raid 5. If no difference I’d rather add the two new drives and let the NAS handle the migration.

I suggest reading more about RAID types. RAID 1 is not the best choice for multiple drives and RAID 5 has its limitations too. You will not be able to mix different size hard drives.
I wonder if QNAP offers different types of RAID configurations?

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Appreciate that input. I’ve spent a good time researching RAID types and feel this meets my needs. I’m really not concerned with space lost (1/2 the space mirroring RAID 1). Nor am I concerned with the performance of RAID 5. Drives are pretty cheap these days so cost is not the main driver.

I’ve been running RAID 1 on two different NASs for 10+ years. Perfect performance for my 2-person household. Never an issue with standard or HighRez music. DVD, Blu-Ray, and 4K movie rips are perfect in 7.2 surround and maximum resolution.

I’m not running a data center in my house more interested in rock solid reliability. I just want to do it once and be done with it.

I have a solid back up plan as well.

All that said I’m still open to exploring options. My constraints are:
4 Bay NAS
4 X Identical Seagate 10TB Ironwolf pro Red drives

Storage only I don’t run Roon or Plex on the NAS itself. Roon is on its own dedicated NUC. Plex is on a Shield Pro.

poking @Graeme_Finlayson to see if this might be in his wheelhouse?

I’m not sure what is your concern in this case. You seem to have enough knowledge to make inform decision.

I’ve read online (dangerous I know) and a fellow Roon user I know just told me he went through the same drill and he concluded that while the consumer devices claim to do smooth migrations they often have continued problems long after.

His advice was to NOT migrate but to start from scratch. One data point. I’m curious if others have experience/advice.

I’m not all that interested in pros/cons of different RAID but specifically if I should let my QNAP migrate from RAID 1 to RAID 5 (easy for me) or rebuild it from scratch…lots of external USB shuffling and days of data copying…All things being equal I’d rather migrate, but if problematic I’m willing to start from scratch.

I think you’d be better off sticking to RAID 1 and adding another mirror to your existing pool. Of course, you’ll only have 20TB total, but re-silvering if something goes wrong is going to be a lot easier to deal with. Likewise, you can go to larger drives with RAID 1 without compromising the information on the drives.

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Funny you mention that. Right now I have various 2, 3, 4TB USB drives connected like a tech-octopus all over my office copy/backing up various iterations of all sorts oft combinations to to be safe. HighRez music on one, 16/44 on another, movies here and there and an extra of music just to make sure.

I’m a bit crunched for time and a lot on my plate. I was wondering if in the short run to do just that; another 10TB Raid 1 for a total of 20 but the new 10 being almost totally free. Plus not needing for the 1 to 5 time as I’m sure that will be long as well.

It would buy me some time to get a larger backup device (or two) that I can do 9-10TB in one shot.

I’m also not happy with the original 10TB’s layout. So if I migrate that RAID 1 to 5 I’ll still have the QNAP default locations (starting at “public”) that I now know how to avoid.

More food for thought I guess. Also, if I have two RAID 1 10TBs in one box and I get my backup more tidy I cold still go RAID 5 with 30TB down the road and no new drives.

I was wondering when someone might pose this question…

TL;DR - you can let the NAS convert from RAID 1 to RAID 5 without a clean install, however, I would strongly advise against RAID 5

Apologies in advance, this is going to be a long post.

Firstly, why do you want/need RAID? This is a really serious question.

RAID is not a backup solution.

I’ll say that again -


Ok, let that sink in for a moment.

There are two reasons for running RAID.

  1. High availability. RAID 1 (2 drives), RAID 5 (3-16 drives), RAID 6 (4+ drives). If a drive fails, you carry on as normal, replace the drive and rebuild the new drive into the array.

  2. High performance. RAID 0 stripe array (2 drives) RAID 10 mirrored stripe array (4 drives or more) You’re reading and writing from multiple drives simultaneously, so performance is higher than a single drive.

OK, different RAID types (maybe you know this already?)

RAID 1- Two drives. Data is mirrored (copied onto both). If one drive fails, you still have your data. Replace the drive, the data is copied to the new drive and carry on as normal.


RAID 5 (striping with parity) - Data blocks are striped across the drives and on one drive a parity checksum of all the block data is written. The parity data are not written to a fixed drive, they are spread across all drives, as the drawing below shows. Using the parity data, the computer can recalculate the data of one of the other data blocks, should those data no longer be available. That means a RAID 5 array can withstand a single drive failure without losing data or access to data.


RAID 6 (striping with double parity) - RAID 6 is like RAID 5, but the parity data are written to two drives. That means it requires at least 4 drives and can withstand 2 drives dying simultaneously. The chances that two drives break down at exactly the same moment are of course very small. However, if a drive in a RAID 5 systems dies and is replaced by a new drive, it takes hours or even more than a day to rebuild the swapped drive. If another drive dies during that time, you still lose all of your data. With RAID 6, the RAID array will even survive that second failure.


RAID 0 - (striping) In a RAID 0 system data are split up into blocks that get written across all the drives in the array. By using multiple disks (at least 2) at the same time, this offers superior I/O performance. This performance can be enhanced further by using multiple controllers, ideally one controller per disk.


RAID 10 - (mirrored stripe, combining RAID 1 and RAID 0) It is possible to combine the advantages (and disadvantages) of RAID 0 and RAID 1 in one single system. This is a nested or hybrid RAID configuration. It provides security by mirroring all data on secondary drives while using striping across each set of drives to speed up data transfers.


The interesting bit

RAID 0 increases performance - simultaneous reading and writing from 2 drives, so it’s twice as fast as 1 drive, but offers ZERO redundancy. Lose a drive, you lose everything.

RAID 1 gives single drive redundancy - if 1 drive fails, you still have your data on the other drive.

RAID 5 gives single drive redundancy - if 1 drive fails, you can replace it and rebuild the array maybe. Read transactions are fast as the data is split over multiple drives. Write transactions are slower than a single drive due to the parity calculations.

RAID 6 gives dual drive redundancy - up to 2 drives can fail and you can still rebuild the array maybe. Read transactions are faster as data is split over multiple drives. Write performance is up to 20% slower than RAID 5.

RAID 10 guarantees single drive redundancy - any one drive can fail and you can still rebuild the array. If a second drive fails, then it’s a game of Russian Roulette. The more drives you have, the lower the chance of a second drive failure killing the array. You have to lose the corresponding mirror drive to the initial failed drive to lose the whole array, so the more drives, the less likely this is. Performance is high - you’re reading and writing to and from multiple drives.

Now for the really interesting (scary) bit

The Achilles heel of RAID 5 and RAID 6 is the URE (unrecoverable read error) rate of your chosen drives. For consumer drives, it’s typically 1 in 10^14 (1 byte in 12.5TB), for enterprise drives, it’s typically 1 in 10^15 (1 byte in 125 TB). If a drive fails, it will be rebuilt using the parity data from the other drives, however, if during rebuild, a URE is encountered, your array will fail to rebuild and you lose the array. The bigger your array size, the higher the likelihood of an array failure during rebuild.

Another thing to note, is that if you lose a drive, your NAS will be CRIPPLED during rebuild. I experienced this with a 4-bay Synology Diskstation. The rebuild period took days and the NAS was essentially unusable during this period.

If you plan on adding 2 x 10TB drives, I would recommend going with RAID 10, you’ll end up with 20TB of storage (which is still HUGE). You gain 2 x read and write speed performance and still have 1 drive redundancy. A rebuild will be much faster. A URE during rebuild is less likely.

I would also recommend additional local backup if you can manage it and I would strongly advise you sort out an off-site backup service if you haven’t already done so. Backblaze/Backblaze B2 is robust and affordable. Recovery of your data is expensive though, which is why additional local backup is crucial.

Yes, RAID 5 will give you 30TB of storage, but the risks in my opinion outweigh the benefits.

My Synology Rackstation runs with 12 x 4TB HDDS in RAID 10 - I have 20.9 (real) TB of storage and it’s still less than half full. It reads and writes faster than an enterpise SSD.

If you want further reading, this link and the links therein are well worth reading.

Sorry for the long post, this stuff is so important and so often misunderstood.


Reorganize your data onto the new mirror. From a practical perspective I wouldn’t recommend other RAID configurations for home unless you hold spare drives. RAID 1 gives you fault tolerance and will continue working if a drive fails. Adding a new drive is straightforward and you still have access to your data. BTW, resilience is not the same as maintaining backups.

FWIW, I use ZFS mirrors and backup these to a local drive and the cloud. Last time I had a drive failure, I was down for a few minutes while swapping in a new drive. Resilvering took some hours but I could still access all my data while this was happening.


Appreciate your lengthy and thoughtful post. For sure will read it a few times and let the things I did not know sink in.

First, while it can never be said enough, I’m VERY aware RAID is not backup. I preach it to anyone who will listen. Thus my post…probably when you were typing your tomb :wink: that I have several “extra” backups going on right now. I have most of my stuff at a friends house too…so I got backup covered. At least I hope so.

If I really reflected I’d guess I landed here out of inertia. Long ago when drives were measured in GB not TB I dug into various RAID-stuff and came to the conclusion I “needed” it. It was the idea of drive failure and rebuilding that appealed to me. Fast forward a bit and I actually had a drive fail back when I had a 2-BAY NAS with 2 X 3TB in RAID 1. Popped in my reserve drive (identical to the other two drives) sitting on a shelf for just that reason. Took about a day to rebuild (probably less than 2TB) and all was good for several more years. So, I’ve just kept on this path and not really thought about it much beyond bigger drives and the desire to get a bit more realized space with 5 over 1 (effectively losing 1/4 vs 1/2). Speed is not an issue…but in the back of my mind faster is always better.

I had zero idea of the URE thing…or I’ve drank/slept since then, and forgotten about it. Thanks a lot for that! I ponied up for better drives (Ironwolf Red) but your point is taken.

If I’m sitting in the middle letting you and @Martin_Webster tug me in each direction my question would be: with 4 X 10TB drives if I’m only going to net 20TB Why/Why not two separate RAID 1’s in the same 4-bay box or 1 RAID 10 in that same box…if I’m understanding you both correctly? Speed for 10, right? Anything else. Two sets of RAID 1 surely seems easy given I already have one.

Appreciate the civil discussion on the Roon forums, as always, and the thoughtful input. Keep it coming.

RAID10 will give you the speed plus one large volume. 2 X RAID 1 gives you the same storage capacity, but over 2 volumes without the speed gain.


I think @Graeme_Finlayson and I are broadly on the same page: go for mirrors. My recommendation is purely practical. You need a degree of resilience, so you keep working when a disk fails. And you have backup covered.

RAID10 is fine, you may not need the performance striping offers, but you still have good redundancy. Also, your 4 x 10 TB drives will give you 20TB; the same as two mirrored pools. If you can implement RAID 10 without starting afresh go for it as this still has the benefits I mentioned.


You can’t beat spare drives - I have a couple of hot spares in my NAS expansion bay and keep at least one cold spare on the shelf.

HDDs/SSDs are consumables - I just wish more people realised that!

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I’d go with RAID 1+0 (RAID10)

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