ReadyNAS OS6 issues with Ultra 4

Hi All,

I'm having trouble with OS6 on latest OS6 firmware and wondering if somebody saw similar issues.

I have Ultra4 with 4x4TB WD Reds. I had no issues on OS4.

Upgrade to latest version went well, but tests showed that data got corrupted (I would copy 200k / 2TB files and than compare md5sums). I tried factory reset and rebuild volume but it didn't help. tried to turn x-RAID off / remove quote  experemt with different protocols to transfer (AFP, NFS, rsync) but all results are consistent

After 2 days of reboots/stress testing it finally gave up with kernel crash

[633273.945339] BUG: unable to handle kernel paging request at 000000100000001c
[633273.946019] IP: [<ffffffff880dd551>] find_get_entry+0x3a/0x69
[633273.946019] PGD 0 
[633273.946019] Oops: 0000 [#1] SMP 
[633273.946019] Modules linked in: vpd(PO)
[633273.946019] CPU: 0 PID: 2247 Comm: afpd Tainted: P           O    4.4.140.x86_64.1 #1
[633273.946019] Hardware name: NETGEAR  ReadyNAS/ReadyNAS , BIOS 080016  09/20/2010
[633273.946019] task: ffff88003d65d400 ti: ffff880005f24000 task.ti: ffff880005f24000
[633273.946019] RIP: 0010:[<ffffffff880dd551>]  [<ffffffff880dd551>] find_get_entry+0x3a/0x69
[633273.946019] RSP: 0018:ffff880005f27c78  EFLAGS: 00010246
[633273.946019] RAX: ffff88001d0af4b0 RBX: ffff88001d140360 RCX: ffff88001d0af4b0
[633273.946019] RDX: ffff88001d0af4b0 RSI: 0000000000073e02 RDI: 0000001000000000
[633273.946019] RBP: ffff880005f27c88 R08: ffff880005f27c60 R09: ffff88001d0af478
[633273.946019] R10: ffff88001d0af4b0 R11: ffffffff88b6449c R12: 0000000000073e02
[633273.946019] R13: ffff88001d140358 R14: 0000000000073e02 R15: 0000000073e00000
[633273.946019] FS:  00007fe51e89b880(0000) GS:ffff88003f000000(0000) knlGS:0000000000000000
[633273.946019] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[633273.946019] CR2: 000000100000001c CR3: 000000000bf92000 CR4: 0000000000000670
[633273.946019] Stack:
[633273.946019]  0000000000000007 000000000342004a ffff880005f27cc8 ffffffff880dd5fe
[633273.946019]  00000000000178a3 0000000000000002 0000000000000002 ffff88001d1401f0
[633273.946019]  ffff8800110d4c10 0000000073e00000 ffff880005f27d30 ffffffff882aa65e
[633273.946019] Call Trace:
[633273.946019]  [<ffffffff880dd5fe>] pagecache_get_page+0x25/0x176
[633273.946019]  [<ffffffff882aa65e>] prepare_pages+0x7b/0x14a
[633273.946019]  [<ffffffff882ab7dc>] __btrfs_buffered_write.isra.6+0x227/0x51b
[633273.946019]  [<ffffffff8809e963>] ? current_fs_time+0x20/0x25
[633273.946019]  [<ffffffff882aedec>] btrfs_file_write_iter+0x2ba/0x3c6
[633273.946019]  [<ffffffff8811c9bd>] __vfs_write+0x9a/0xc3
[633273.946019]  [<ffffffff8811d0ce>] vfs_write+0xb6/0x160
[633273.946019]  [<ffffffff8811dc09>] SyS_pwrite64+0x5c/0x7b
[633273.946019]  [<ffffffff888e540a>] entry_SYSCALL_64_fastpath+0x1e/0x8e
[633273.946019] Code: 89 e6 48 89 df e8 e3 8a 28 00 48 85 c0 48 89 c1 74 41 48 8b 38 48 85 ff 74 39 40 f6 c7 03 74 0b 40 f6 c7 01 75 d9 48 89 f8 eb 2a <8b> 57 1c 85 d2 74 cd 8d 72 01 89 d0 f0 0f b1 77 1c 39 c2 74 04 
[633273.946019] RIP  [<ffffffff880dd551>] find_get_entry+0x3a/0x69
[633273.946019]  RSP <ffff880005f27c78>
[633273.946019] CR2: 000000100000001c
[633274.291068] ---[ end trace cc1296c118ab43b8 ]---

So it looks like there's some compatibility issue. I ordered new memory module to see if it could be the problem but ti's highly unlikely.

I tried to downgrade to 6.9.3 and it's more stable, but after 1+day of stress testing it also gave up and netgear daemon stoped working. I was able to ssh into the box, there were not kernel crashed but the daemoung has crashed with segfault on restart. 

After reboot, system went through initialization and I got to the wizard.

So from my side I have 2 questions, does anyone run legacy model pro4/6 ultra4/6 with WD REDs on OS6 ? if yes what version.

second is how to downgrade back to OS4 ? I found couple link on this forum but all of them are dead