Hooray, slut truly yours formerly known as systemschlampe@taz.de is back at administrating system! [More due to it needing to be done rather than due to coronavirus quarantine!]
Getting an affordable smooth external OpenZFS loss-protected self-repairing integrity- and redundancy-checked storage expansion running turned out merely as simple as
aptitude install zfs-initramfs && zpool create zfs raidz1 /dev/sd?9 && zfs set compression=lz4 dedup=on zfs && rsync -av /xfs/ /zfs/
after more elaborately having upgraded my initial Debian8=oldoldstable“jessie„ step-by-step to Debian11=experimental“bullseye„ on my FreeDOS–Lenovo G505 and having partitioned my 3×4001GB@USB3-B:A 1TEAPF-500 Seagate Expansion Portable Drives for 80€/4TB each whose serial numbers most easily mnemonized as ending in Y (sdd) O (sdc) N (sdb) can be found printed underneath and showing up in file:/dev/disk/by-partlabel/ like this
==> /etc/fdisk/A.fdisk <== label: dos label-id: 0x172d5219 device: /dev/sda unit: sectors /dev/sda1 : start= 2048, size= 610666496, type=83, bootable /dev/sda2 : start= 610670590, size= 14471170, type=5 /dev/sda5 : start= 610670592, size= 14471168, type=82 ==> /etc/fdisk/N.fdisk <== label: gpt label-id: 3B78AFC5-80AB-4763-A2F6-66DDF506633C device: /dev/sdb unit: sectors first-lba: 34 last-lba: 7814037133 /dev/sdb1 : start= 2048, size= 2097152, type=C12A7328-F81F-11D2-BA4B-00A0C93EC93B, uuid=9BA008CC-865B-4982-BEBE-8BF3B7DE52A3, name="N" /dev/sdb2 : start= 2099200, size= 16777216, type=49F48D32-B10E-11DC-B99B-0019D1879648, uuid=C53802C5-0D17-4601-9A0F-B7B1F97038FB, name="bsdswap" /dev/sdb3 : start= 18876416, size= 50331648, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=86DFEB4C-E5FC-4A13-A39F-78EC316DB37F, name="deepin" /dev/sdb4 : start= 69208064, size= 16777216, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=87BB2F7B-01CC-4D5E-8504-6A3A7B8DC7E7, name="galliumos" /dev/sdb5 : start= 85985280, size= 25165824, type=516E7CB4-6ECF-11D6-8FF8-00022D09712B, uuid=55124518-0418-444D-BF6C-0FC476B4D77F, name="freebsd" /dev/sdb6 : start= 111151104, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=6AD468FD-DDAC-4E40-9A0D-4272DF21FA7F, name="archlinux" /dev/sdb7 : start= 178259968, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=33E6C903-79AD-4AEB-925B-3E41BD7F4A2D, name="funtoo" /dev/sdb8 : start= 245368832, size= 25165824, type=85D5E45A-237C-11E1-B4B3-E89A8F7FC3A7, uuid=A1281AE6-FDA7-4602-9D92-D13EC2429E07, name="hammer2n" /dev/sdb9 : start= 270534656, size= 7340079104, type=516E7CBA-6ECF-11D6-8FF8-00022D09712B, uuid=617E2D40-8510-4B6D-BDFF-E67215BAC5FA, name="zfs5n" /dev/sdb10 : start= 7610613760, size= 2097152, type=C91818F9-8025-47AF-89D2-F030D7000C2C, uuid=CA986527-ECDD-4F4D-B1EE-024CCDC18FD9, name="plan9" /dev/sdb11 : start= 7612710912, size= 6291456, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=EAC571FA-7EF8-404F-A0A2-5E36CD5E6106, name="alpine" /dev/sdb12 : start= 7619002368, size= 60817408, type=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7, uuid=590F7AE9-1CC3-48E4-B189-BE703AC19D28, name="umsdos" /dev/sdb13 : start= 7679819776, size= 2097152, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=CFD81C05-5AD9-4568-B393-E8A863C5DD05, name="gparted" /dev/sdb14 : start= 7681916928, size= 4194304, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=6BC4B24F-4B80-43B9-9C9A-5B6D51B73016, name="knoppix" /dev/sdb15 : start= 7686111232, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=3A51DD14-45A6-4A57-BED7-757BEA2B4286, name="nixos" /dev/sdb16 : start= 7753220096, size= 25165824, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=3D3515D0-6843-41E5-9C0B-388111C37CEF, name="reiser4n" /dev/sdb17 : start= 7778385920, size= 16777216, type=516E7CB6-6ECF-11D6-8FF8-00022D09712B, uuid=42D16E7D-A730-4262-B948-78B5714028C3, name="ufs2n" /dev/sdb18 : start= 7795163136, size= 18873998, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=F67E1998-D4ED-4BF5-959C-EEEBCF142E0A, name="xfs5n" ==> /etc/fdisk/O.fdisk <== label: gpt label-id: 2E4F9FA6-37F8-4E6A-A868-C2A6D7A954BB device: /dev/sdc unit: sectors first-lba: 34 last-lba: 7814037133 /dev/sdc1 : start= 2048, size= 2097152, type=C12A7328-F81F-11D2-BA4B-00A0C93EC93B, uuid=E37CFA0C-40B5-4FC2-BDB1-57E6A2C37141, name="O" /dev/sdc2 : start= 2099200, size= 16777216, type=0657FD6D-A4AB-43C4-84E5-0933C84B4F4F, uuid=BF8CF253-C803-46AB-B4FE-B82A77F8C7B1, name="linuxswap" /dev/sdc3 : start= 18876416, size= 50331648, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=51576F51-427E-4422-AD87-9D7B38D64335, name="deepin" /dev/sdc4 : start= 69208064, size= 16777216, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=09E16FEC-442A-4BAA-A191-E8211C03835B, name="galliumos" /dev/sdc5 : start= 85985280, size= 25165824, type=49F48D5A-B10E-11DC-B99B-0019D1879648, uuid=F191E3D1-DBB1-4832-8154-463E546FE8C4, name="netbsd" /dev/sdc6 : start= 111151104, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=08B103C1-C396-402F-92F5-9D76EAEC24F0, name="L\xce\xa3\xce\x94" /dev/sdc7 : start= 178259968, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=E37C8388-2BF7-4F9D-9951-1AC96C813CBD, name="gentoo" /dev/sdc8 : start= 245368832, size= 25165824, type=85D5E45A-237C-11E1-B4B3-E89A8F7FC3A7, uuid=DA15C747-D067-4C90-95DA-3206401491CC, name="hammer2o" /dev/sdc9 : start= 270534656, size= 7340079104, type=516E7CBA-6ECF-11D6-8FF8-00022D09712B, uuid=1CE58DA7-55DB-4D1E-847A-7604F1CDE8C7, name="zfs5o" /dev/sdc10 : start= 7610613760, size= 2097152, type=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7, uuid=B683CF84-4DD4-4E59-A7B6-58AD4C3F7CFC, name="freedos" /dev/sdc11 : start= 7612710912, size= 6291456, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=5C074992-17E8-4735-BD52-41FB03B2608E, name="stali" /dev/sdc12 : start= 7619002368, size= 60817408, type=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7, uuid=2BE476FA-1FA9-43C3-9631-702164FAADC9, name="vfat" /dev/sdc13 : start= 7679819776, size= 2097152, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=3ACAD615-28EA-44AD-8DED-44363FDB52ED, name="hurd" /dev/sdc14 : start= 7681916928, size= 4194304, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=87B585C2-F10F-42AB-88A1-1E7D8E290A22, name="kali" /dev/sdc15 : start= 7686111232, size= 67108864, type=824CC7A0-36A8-11E3-890A-952519AD3F61, uuid=EAF80B9B-2DE8-4004-9C46-D1FF08C0A465, name="openbsd" /dev/sdc16 : start= 7753220096, size= 25165824, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=9342E761-9C73-4A26-87EA-9A5DF514522A, name="reiser4o" /dev/sdc17 : start= 7778385920, size= 16777216, type=516E7CB6-6ECF-11D6-8FF8-00022D09712B, uuid=10DD6BD7-B6CE-4A24-AD37-11DD97DF9A1B, name="ufs2o" /dev/sdc18 : start= 7795163136, size= 18873998, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=895FDBFE-1813-4D59-9EE5-963091228B4C, name="xfs5o" ==> /etc/fdisk/Y.fdisk <== label: gpt label-id: B9AF30AC-429C-4B18-BB06-CFE67C7AC239 device: /dev/sdd unit: sectors first-lba: 34 last-lba: 7814037133 /dev/sdd1 : start= 2048, size= 2097152, type=C12A7328-F81F-11D2-BA4B-00A0C93EC93B, uuid=BC9D80EE-0BB2-43F6-A238-CE7B9BDEDDC9, name="Y" /dev/sdd2 : start= 2099200, size= 16777216, type=516E7CB5-6ECF-11D6-8FF8-00022D09712B, uuid=96FA11D0-5C1D-4196-B548-703943A94561, name="L2ARC" /dev/sdd3 : start= 18876416, size= 50331648, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=D477D747-9F83-4612-895C-733D0C720AB3, name="edubuntu" /dev/sdd4 : start= 69208064, size= 16777216, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=C81C4583-F079-4D97-B73B-6DF5D4348B06, name="trisquel" /dev/sdd5 : start= 85985280, size= 25165824, type=516E7CB4-6ECF-11D6-8FF8-00022D09712B, uuid=94739769-E35B-4666-BC46-48BACBDA9272, name="dragonfly" /dev/sdd6 : start= 111151104, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=B15C5C76-3411-447E-A51B-F81ED4E2C1F9, name="aryalinux" /dev/sdd7 : start= 178259968, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=D332097F-211C-4FC6-B333-7F6B053BD215, name="chromiumos" /dev/sdd8 : start= 245368832, size= 25165824, type=85D5E45A-237C-11E1-B4B3-E89A8F7FC3A7, uuid=85124340-D23C-41B0-986C-DB077EB94EC6, name="hammer2y" /dev/sdd9 : start= 270534656, size= 7340079104, type=516E7CBA-6ECF-11D6-8FF8-00022D09712B, uuid=5424C876-2B86-4BB2-BC96-AE85C86E50A7, name="zfs5y" /dev/sdd10 : start= 7610613760, size= 2097152, type=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7, uuid=08C537CC-3B88-441A-AD54-AF0990C409BD, name="minix3" /dev/sdd11 : start= 7612710912, size= 6291456, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=D9F2E4F7-4DF9-4186-86A3-D213AD1AF121, name="gittup" /dev/sdd12 : start= 7619002368, size= 60817408, type=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7, uuid=67A3D163-2FE7-4ED7-8895-AC7C16D238B3, name="ntfs" /dev/sdd13 : start= 7679819776, size= 2097152, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=DA011063-9BBE-4733-A8D0-CDA79E9194D5, name="systemrescue" /dev/sdd14 : start= 7681916928, size= 4194304, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=F842B89D-EA94-47B6-B77C-EC1847440349, name="tails" /dev/sdd15 : start= 7686111232, size= 67108864, type=4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709, uuid=736DBC54-2291-4B2F-AE14-69B9AFB152F5, name="guixsd" /dev/sdd16 : start= 7753220096, size= 25165824, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=AA600A6D-0B62-4677-AFF2-EE5F68CFD98B, name="reiser4y" /dev/sdd17 : start= 7778385920, size= 16777216, type=516E7CB6-6ECF-11D6-8FF8-00022D09712B, uuid=0EF85BBF-3401-48EE-9968-D3377F8F9D63, name="ufs2y" /dev/sdd18 : start= 7795163136, size= 18873998, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=F8ECFBFF-E0A0-4E3F-A6AA-1F52C6D33771, name="xfs5y"