Hi all, My Synology NAS (a very old DS508) awaken this morning with a severe disk failure: 3 out of 5 disks failed at once. It uses RAID 6, thus I'm not able to gracefully recover the data using the standard Synology tools. I disassembled the box, cleaned the SATA slots and all electric plugs/sockets and the disks are being recognized again, but the RAID volume displays as crashed and its data is not accessible. The dmesg log shows this: [ 38.762338] md: md2 stopped. [ 38.799568] md: bind<sda3> [ 38.802723] md: bind<sdb3> [ 38.807089] md: bind<sdc3> [ 38.811295] md: bind<sdd3> [ 38.816123] md: bind<sde3> [ 38.818918] md: kicking non-fresh sdd3 from array! [ 38.823766] md: unbind<sdd3> [ 38.826649] md: export_rdev(sdd3) [ 38.829978] md: kicking non-fresh sdc3 from array! [ 38.834773] md: unbind<sdc3> [ 38.837653] md: export_rdev(sdc3) [ 38.840976] md: kicking non-fresh sdb3 from array! [ 38.845770] md: unbind<sdb3> [ 38.848650] md: export_rdev(sdb3) [ 38.851973] md: kicking non-fresh sda3 from array! [ 38.856767] md: unbind<sda3> [ 38.859657] md: export_rdev(sda3) [ 38.876922] raid5: device sde3 operational as raid disk 4 [ 38.883676] raid5: allocated 5262kB for md2 [ 38.899483] 4: w=1 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0 [ 38.904454] raid5: raid level 6 set md2 active with 1 out of 5 devices, algorithm 2 [ 38.912141] RAID5 conf printout: [ 38.915366] --- rd:5 wd:1 [ 38.918071] disk 4, o:1, dev:sde3 [ 38.921544] md2: detected capacity change from 0 to 8987271954432 [ 38.973111] md2: unknown partition table Naively, I searched a bit and found that I could add the disks back to the array, and did this: mdadm /dev/md2 --fail /dev/sda3 --remove /dev/sda3 mdadm /dev/md2 --add /dev/sda3 mdadm /dev/md2 --fail /dev/sdb3 --remove /dev/sdb3 mdadm /dev/md2 --add /dev/sdb3 mdadm /dev/md2 --fail /dev/sdc3 --remove /dev/sdc3 mdadm /dev/md2 --add /dev/sdc3 mdadm /dev/md2 --fail /dev/sdd3 --remove /dev/sdd3 mdadm /dev/md2 --add /dev/sdd3 However, the disks where added as spares and the volume remained crashed. Now I'm afraid that such commands have erased metadata and made things worse... :-( Is there a way to reconstruct the array and to recover its data, at least partially? (The most relevant data was backed up, but there are some TB of movies and music that I would be glad to recover). The NAS was mostly used for file reading (serving media files to the local network). Contents of /proc/mdstat (after the commands above): Personalities : [raid1] [linear] [raid0] [raid10] [raid6] [raid5] [raid4] md2 : active raid6 sda3[0](S) sdb3[1](S) sdc3[2](S) sdd3[3](S) sde3[4] 8776632768 blocks super 1.2 level 6, 64k chunk, algorithm 2 [5/1] [____U] md1 : active raid1 sda2[1] sdb2[2] sdc2[3] sdd2[0] sde2[4] 2097088 blocks [5/5] [UUUUU] md0 : active raid1 sda1[1] sdb1[2] sdc1[3] sdd1[0] sde1[4] 2490176 blocks [5/5] [UUUUU] unused devices: <none> Output of mdadm --detail /dev/md2 (also after the commands above) /dev/md2: Version : 1.2 Creation Time : Sat Sep 5 12:46:57 2020 Raid Level : raid6 Array Size : 8776632768 (8370.05 GiB 8987.27 GB) Used Dev Size : 2925544256 (2790.02 GiB 2995.76 GB) Raid Devices : 5 Total Devices : 5 Persistence : Superblock is persistent Update Time : Sun Jun 6 22:48:34 2021 State : clean, FAILED Active Devices : 1 Working Devices : 5 Failed Devices : 0 Spare Devices : 4 Layout : left-symmetric Chunk Size : 64K Name : DiskStation:2 (local to host DiskStation) UUID : dcb32778:c99523d8:2efdeb61:54303019 Events : 78 Number Major Minor RaidDevice State 0 0 0 0 removed 1 0 0 1 removed 2 0 0 2 removed 3 0 0 3 removed 4 8 67 4 active sync /dev/sde3 0 8 3 - spare /dev/hda3 1 8 19 - spare /dev/sdb3 2 8 35 - spare /dev/hdc3 3 8 51 - spare /dev/sdd3 Best regards and many thanks for any help! Carlos
