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Issue adding drive 4 to ReadyNAS nv+ v2
All
I recently setup my ReadyNAS NV+ v2 from scratch with 3 3 TB Hitachi DK7SAD300 drives. The steps I followed and an issue I encountered are described in
Best way to swap drives ReadyNAS nv+ v2 | NETGEAR Communities (https://community.netgear.com/discussions/readynas-use/best-way-to-swap-drives-readynas-nv-v2/2473844).
After restoring all data back on the NAS, I added drive 4 of identical specifications. Note that I previously tested all drives with CrystalDiskInfo to make sure they were fine. And I performed a full erase using WD's KitFox.
For reasons I do not understand, the RAID volume md2 (corresponding with volume C) does not behave the way it should. Specifically:
- When I first added disk 4 (while the NAS was powered down - i.e. a cold add), it only created partitions sdd1 and sdd2. sdd3 that was supposed to have been added to md2 as device number 4 was never created, this is also confirmed by system.log. When examining the partition table using gdisk, it only shows sdd1 and sdd2 only.
- Performing a "hot" remove and add of disk 4 had the exact same result as (1).
- While it might appear logical that there's somehow an issue with disk 4, I proceeded by performing a "hot" remove and add of disk 2. This time, all 3 partitions sdd1, sdd2 and sdd3 were created. However, on disk 2 only sdb1 and sdb2 were present somehow (what happened to sdb3?). As a result, a sync was automatically performed for md2. Once complete, md2 consisted of partitions sda3, sdc3 and sdd3.
- At least (3) rules out an issue with disk 4. I proceeded by performing a "hot" remove and add of disk 3. This time, all 3 partitions sdb1, sdb2 and sdb3 were created. However, on disk 3 only sdc1 and sdc2 were present somehow (what happened to sdc3?). As a result, a sync was automatically performed for md2. Once complete, md2 consisted of partitions sda3, sdb3 and sdd3.
You can clearly see that the most recent drive hot added is missing its third partition using gdisk:
Clearly, there's a pattern here. The disk that has been hot added last loses its third partition somehow. I know this NAS is no longer supported, my next options include:
- (a) Following the steps described in Disk not resyncing | NETGEAR Communities (https://community.netgear.com/discussions/readynas-use/disk-not-resyncing/871010) to manually create the third partition sdc3 on disk 3. Hopefully, this will trigger the partition to be added to the md2 volume (and lead to an increase in capacity of the volume).
- (b) Performing a reinstall of the OS without destroying the data on md2.
- (c) Backing up all data and perform a destructive reinstall of the OS destroying all data including on md2.
Would appreciate your thoughts here!
Note: had some issues including all relevant details here in this post, so a more complete story with logs is available in Issue adding 4th drive to ReadyNAS nv+ v2.pdf):
https://www.dropbox.com/scl/fi/6g5jx1xea4r2tjym78cd9/Issue-adding-4th-drive-to-ReadyNAS-nv-v2.pdf?rlkey=p91y2546znenxejecnmwy82ug&st=tg7uza04&dl=0
6 Replies
The disk that has been hot added last loses its third partition somehow.
When you hot-add a disk, the NAS first formats it, and then creates the partitions, and finally resyncs. (This happens no matter how you add the new disk).
So what is happening here is that the NAS is choosing not to recreate the third partition after the format. The partition is not "getting lost". Usually that is a result of the NAS deciding that expanding the array is not possible.
I think your best option is to do a factory default with all disks in place, and see if you get different behavior. That might also resolve your issue with the OS partition RAID group. You would need to restore from backup afterwards. Not sure if that is what you meant by a "destructive install of the OS" or not.
Your option (b) would only have an effect if the OS was somehow corrupted - there is no indication that has happened. It shouldn't make any difference, but it is easy to try.
Option (a) is for a completely different NAS model. That said, manually creating the third partition and rebooting the NAS might work. If you do this on a PC, then make sure you power down the NAS before removing the drive, and leave it powered down until the disk is re-inserted.
Thanks StephenB obviously I am trying to avoid having to do a factory default with all 4 disks in place (as it would require another copy of the approximately 2.6 TB of data to be taken). And yes, I referred to that as (c) / destructive install of the OS.
So I think I understand the behavior now, any hot adding of a disk is destructive (disk will be formatted and new partitions created - followed by a sync). A cold add would be different, i.e. if you power down your NAS remove a disk to (say) add a partition and insert it again before powering it on it would not trigger a format operation and creation of fresh partitions.
I was considering (a) while from the NAS itself, i.e. without adding/removing any of the disks. Based on what we're seeing though, it indeed appears that the NAS somehow does not create the third partition for a reason. Could this be because we would otherwise exceed the size of the md2 volume?
Thinking about the fresh install I performed, I recall it created the volume md2 and next performed a sync. Maybe it created the volume with two drives, adding the third drive through the sync shortly afterwards? That would imply that the capacity of the md2 volume started at the size of a single disk (2.7 TB). I recall as per
Maximum disk size for ReadyNAS NV+ V2 | NETGEAR Communities
that volumes cannot increase by more than 8 TB from their size at creation, nor can they increase beyond 16 TB regardless. Could it be that disk 4 takes us from a raw volume capacity of 2.7 TB to 10.8 TB (i.e. in excess of the max 8 TB increase)?
I always thought this all applied to net capacity of a volume; in that case we would only be hitting the limit if our starting volume size would have been 2.7 TB. I recall having three out of four drives installed in the NAS when I installed it from scratch using the RAIDar software. But not sure now, I think the original logs in /var/log might already have gone?
I believe it would be helpful if we could see whether we are hitting a maximum or not somehow from a log. I.e. an explanation for why the third partition of a hotly added disk never gets created.
A cold add would be different, i.e. if you power down your NAS remove a disk to (say) add a partition and insert it again before powering it on it would not trigger a format operation and creation of fresh partitions.
Not necessarily different. If the NAS detects the disk as new (unformatted or not already in the volume), it goes through the same process. And it normally will do that with cold add.
If you want to try to create the partition manually, it'd be best to do with with the NAS running, and then manually enter the commands to expand the RAID group and then the file system.
Maximum disk size for ReadyNAS NV+ V2 | NETGEAR Communities
that volumes cannot increase by more than 8 TB from their size at creation, nor can they increase beyond 16 TB regardless. Could it be that disk 4 takes us from a raw volume capacity of 2.7 TB to 10.8 TB (i.e. in excess of the max 8 TB increase)?Your logs show three disks on 31 January, I have no way to see anything before that.
But even if you started with 1 disk installed, the total gain in volume size would be 6 TB (5.45 TiB). The limits are not computed from raw disk sizes. A single 3 TB drive would give you a 2.7 TiB volume size, and a 4x3TB RAID-5 setup gives you an 8.18 TiB volume size.
So you are not hitting any of the expansion limits.
obviously I am trying to avoid having to do a factory default with all 4 disks in place (as it would require another copy of the approximately 2.6 TB of data to be taken).
I get that, but I still think that is the right next step.
I just found the original /var/log/frontview/raid_config_2026_01_31.log, this confirms the that volume md2 was originally setup with 3 drives/partitions.
What I also recall now is that the first time I added disk 4 afterwards, I did so after powering down the NAS (thinking that hot-add was not something that would be supported or would be a bad idea). Maybe this explains why the setup ended up where we are today?
***** RAID configuration log from 2026/01/31 *****
***** mdadm -D --scan -v *****
***** mdadm -D --scan -vv *****
***** mdconfig *****
Device : /dev/md0
Create Time : 1769872583
Update Time : 1769902702
RAID Level : 1
RAID Capacity : 4193268
Disk Size : 4193268
Chunk Size : 0
Disks : 3
RAID Disks : 3
Active Disks : 3
Working Disks : 3
Failed Disks : 0
Spare Disks : 0
State : 1 [ Clean ]
Disk Device RAID Disk Maj/Min Sectors State
---------------------------------------------------------------------------
0 /dev/sda1 0 8/ 1 8388608 6 [ Active Sync ]
1 /dev/sdb1 1 8/17 8388608 6 [ Active Sync ]
2 /dev/sdc1 2 8/33 8388608 6 [ Active Sync ]
Device : /dev/md1
Create Time : 1769872583
Update Time : 1769902459
RAID Level : 1
RAID Capacity : 524276
Disk Size : 524276
Chunk Size : 0
Disks : 3
RAID Disks : 3
Active Disks : 3
Working Disks : 3
Failed Disks : 0
Spare Disks : 0
State : 1 [ Clean ]
Disk Device RAID Disk Maj/Min Sectors State
---------------------------------------------------------------------------
0 /dev/sda2 0 8/ 2 1048576 6 [ Active Sync ]
1 /dev/sdb2 1 8/18 1048576 6 [ Active Sync ]
2 /dev/sdc2 2 8/34 1048576 6 [ Active Sync ]
Device : /dev/md2
Create Time : 1769872584
Update Time : 1769902675
RAID Level : 5
RAID Capacity : 0
Disk Size : 0
Chunk Size : 65536
Disks : 3
RAID Disks : 3
Active Disks : 2
Working Disks : 3
Failed Disks : 0
Spare Disks : 1
State : 1 [ Clean ]
Disk Device RAID Disk Maj/Min Sectors State
---------------------------------------------------------------------------
0 /dev/sda3 0 8/ 3 4294967295 6 [ Active Sync ]
1 /dev/sdb3 1 8/19 4294967295 6 [ Active Sync ]
2 /dev/sdc3 2 8/35 4294967295 0 [ Standby ]
What I also recall now is that the first time I added disk 4 afterwards, I did so after powering down the NAS (thinking that hot-add was not something that would be supported or would be a bad idea). Maybe this explains why the setup ended up where we are today?
That doesn't explain the problem, the expansion should have worked. The NAS is supposed to detect a new disk from a cold start, and even if that didn't work properly the NAS still should have formatted again and expanded when you hot-added it later.
Starting over with all disks in place might (hopefully will) work properly.
I found what I believe is the right log file to keep an eye on: /var/log/frontview/md_expand.log.
Since attaching does not work, here's a copy on dropbox:
https://www.dropbox.com/scl/fi/hleu36aha09opf34w0fay/expand_md.log?rlkey=2auhzx3ptrfee8b7xxy8plgrt&st=l6o7rqpb&dl=0
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