On 11/07/21 04:12, David T-G wrote: > Wol, et al -- > > ...and then Wols Lists said... > % > > > % > % Mirroring as you plan here is okay. > > That's good. Of course, that then makes me scratch my head a bit since > it's still paired with other and needs to not blow up ... I'll have to > back and read more to see why mirror is safe. > Mirroring is safe because, whatever happens to the mirror, you only need one disk to recover. So if the raid falls apart your data is not in danger. > > % > ... > % > and also two 500G drives > % > > % > jpo:~ # parted /dev/sdc print > % > Model: ATA WDC WD5000AAVS-0 (scsi) > ... > % > jpo:~ # smartctl -i /dev/sdc > ... > % > Model Family: Western Digital Caviar Green > ... > % > that I plan to stripe together to use to protect the first. The Caviars > % > are listed as variable speed, but in practice they apparently are just > % > 5400 rpm, so I'd like to take advantage of striping to make them as fast > % > as possible. > % > % Caviar Green ??? Caviars should be okay, but the "green" moniker makes > > Yeah, I'm not too happy about that ... Supposedly they will vary speed > based on demand, so they can deliver 7200rpm performance, but apparently > they always stay at 5400rpm and so they're just basic drives. Meh. > > > % me nervous. Check SCT/ERC, but striping/mirroring will be fine. > > More of that confusion stuff :-) but happy. > > > % > % > This isn't the black magic ;-) of RAID10-on-two-drives, > % > so I don't have to think of one as "front" and one as "back", but do I > % > want more than one partition on each to stripe 4 or 6 slices to avoid > % > hammering on one, or do I just go with each device as a whole and let > % > mdadm handle the magic for me? > % > > ... > % Okay, the simple approach. > % > % Create a single-device mirror using the 1TB and the special device > % "missing". Copy everything across and make sure it's all okay. (I'm > % assuming you can safely wipe this drive as it has nothing on it you wish > % to keep.) > > Correct. > > > % > % Create a striped device using the two 500GB drives. > > That's the fun part ... I'm thinkin' I'm just going to have to do sector > math to predict how large the new dev can be so that I can back into a > proper partition size on the 1T so that both halves can match. Do you need the entire space? Can you create a 900GB mirror on the 1TB? You can always grow the mirror and the filesystem later. > > > % > % Plan to replace all the disks with something like Seagate Ironwolves or > % Toshiba N300s in the near future :-) > > Actually, I have four Seagate 4T drives > > diskfarm:~ # parted /dev/sdd print > Model: ATA ST4000DM000-1F21 (scsi) > Disk /dev/sdd: 4001GB > Sector size (logical/physical): 512B/4096B > Partition Table: gpt > Disk Flags: > > Number Start End Size File system Name Flags > 1 1049kB 4001GB 4001GB xfs ata-ST4000DM000-1F2168_W300EYNA raid > 2 4001GB 4001GB 134MB reiserfs wwn-0x5000c50069a8d76f > > diskfarm:~ # smartctl -i /dev/sdd > smartctl 7.0 2019-05-21 r4917 [x86_64-linux-5.3.18-lp152.63-default] (SUSE RPM) > Copyright (C) 2002-18, Bruce Allen, Christian Franke, www.smartmontools.org > > === START OF INFORMATION SECTION === > Model Family: Seagate Desktop HDD.15 > Device Model: ST4000DM000-1F2168 > Serial Number: W300EYNA > LU WWN Device Id: 5 000c50 069a8d76f > Firmware Version: CC52 > User Capacity: 4,000,787,030,016 bytes [4.00 TB] > Sector Sizes: 512 bytes logical, 4096 bytes physical > Rotation Rate: 5900 rpm > Form Factor: 3.5 inches > Device is: In smartctl database [for details use: -P show] > ATA Version is: ATA8-ACS T13/1699-D revision 4 > SATA Version is: SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s) > Local Time is: Sat Jul 10 21:38:12 2021 UTC > SMART support is: Available - device has SMART capability. > SMART support is: Enabled > > in another machine that I plan to upgrade to larger disks and hand down > to this one. They're older, and they don't > > diskfarm:~ # smartctl -l scterc /dev/sdd > smartctl 7.0 2019-05-21 r4917 [x86_64-linux-5.3.18-lp152.63-default] (SUSE RPM) > Copyright (C) 2002-18, Bruce Allen, Christian Franke, www.smartmontools.org > > SCT Error Recovery Control command not supported > > have SMART error handling, but at least they aren't SMR :-) > They're no better! "SCT Error Recovery Control command not supported". This is the red flag. This is the same problem as with the Barracudas. > > % > % https://raid.wiki.kernel.org/index.php/Linux_Raid > % > % Read especially the page on timeout mismatch as this DOES apply to your > % Barracuda !!! > > I'll go back again :-) > And it applies to your 4TBs as well. I wouldn't worry too much - I'm running a mirror on two 3TB Barracudas (I wouldn't have bought them if I'd realised, but I was a raid newbie back then ...) Cheers, Wol
