ReadyNAS NV+ (RND4000) new disk, compatible list?

Yes 4 x 2TB disks is the max supported by the NV+ (v1). When the NV+ was released 2TB disks were still long away from being released. If you're using the default X-RAID (which on Sparc ReadyNAS such as your NV+ v1 uses RAID-4 actually with a dedicated parity disk) it'll automatically handle going from 1 disk to 2 disks to 3 disks to 4 disks and expand the volume to use the capacity of the smallest disk on each disk (of course to get the volume capacity you'd get (n - 1) * capacity of smallest disk, so with 2TB disks it would be (4 - 1) * 2 = 3 * 2 = 6).

Note that disk manufacturers use TB whereas like most computers do our NAS units measure space using TiB (but call it TB). So 6TB is about 5.4TiB. It's still the same amount of space (1KB = 1000 Bytes vs 1 KiB = 1024 Bytes).

No the NV+ v2 is a very different product. It's confusing that it's named so similar to the v1. You can't move from the v1 to the v2 or vice versa. They use a different CPU architecture, different RAID format and different firmware.

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pakarinj wrote:
Hello, I'm have to say I am very disappointed to know that the limitation is 2TB. 

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It's a 12 year hardware design, and it was discontinued 7 years ago.  It is what it is.  The 2TB limit hasn't been hidden, it has certainly been repeated here (and elsewhere) many times.  But I agree that it would have been better if they had put this limitation into the manuals back when the larger drives came onto the market.

That said, it's been a very reliable product for me.  Mine is still in service as a backup (it's too slow and doesn't have enough capacity to be my main NAS any more).

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pakarinj wrote:
 Could you provide information for me how I can change from RAID 1 (2 disks with 2 TB capasity) to RAID 5 with 4 disks? What is the easy way? 

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If you are in XRAID (the default mode), you hot-insert a third 2 TB disk (while the system is running).  The system will convert to 3x2TB RAID-5.  When Frontview says the resync is complete, hot-insert the fourth disk.

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pakarinj wrote:
 Another question is can I upcrade the NV+ v1 to v2? 

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The v2 was discontinued 5 years ago, so you can't purchase a new one.  There was no way to upgrade the hardware, it was completely different inside.  I don't recommend getting a used v2, you'd be better off going to an OS-6 ReadyNAS.

The current entry-level 4-bay ReadyNAS is the RN214, which can handle 4 TB drives (and much larger).  It's also a lot faster than the NV+ v1 and has a lot of features that the NV+ v1 doesn't have.  The next tier up is the RN420 series.  You can't migrate your disks to any of the new ReadyNAS; you'd have to do a clean install which would reformat them.