I’m in the process of building a new NAS server to replace our existing one which is getting a bit long in the tooth. As usual I’ve opted to install Ubuntu Server LTS as the OS. In my current NAS I’ve got the system partition RAID 1’d across all the drives, this means that should one fail I’ve still got 4 copies.<\/p>\n
Setting up the new NAS I’ve put the system partition on a separate SSD from the main data drives. I’ve currently only got the one SSD but I wanted the option of RAID 1’ing the system drive for redundancy should I decide to get another SSD in future.<\/p>\n
The Ubuntu installer will quite happily let you create a RAID 1 MD device with 2 disks but only select a single drive to belong to it. This would be the equivalent of the following mdadm command: Update Time : Fri Jan 16 21:26:58 2015 Name : lupin:2 (local to host lupin) Number Major Minor RaidDevice State Update Time : Fri Jan 16 21:32:17 2015 Name : lupin:2 (local to host lupin) Number Major Minor RaidDevice State I’m in the process of building a new NAS server to replace our existing one which is getting a bit long in the tooth. As usual I’ve opted to install Ubuntu Server LTS as the OS. In my current NAS I’ve got the system partition RAID 1’d across all the drives, this means that should […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[5,28],"tags":[35,34],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p2Rw4E-28","jetpack_sharing_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/posts\/132"}],"collection":[{"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/comments?post=132"}],"version-history":[{"count":2,"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/posts\/132\/revisions"}],"predecessor-version":[{"id":134,"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/posts\/132\/revisions\/134"}],"wp:attachment":[{"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/media?parent=132"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/categories?post=132"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/simon.aldrich.cc\/blog\/wp-json\/wp\/v2\/tags?post=132"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\n
\nmdadm --create \/dev\/md2 --level=1 --raid-devices=2 \/dev\/loop1 missing
\n<\/code>
\nHowever, when you boot the OS will consider that array degraded:
\n
\nmdadm -D \/dev\/md2
\n\/dev\/md2:
\nVersion : 1.2
\nCreation Time : Fri Jan 16 21:24:44 2015
\nRaid Level : raid1
\nArray Size : 32704 (31.94 MiB 33.49 MB)
\nUsed Dev Size : 32704 (31.94 MiB 33.49 MB)
\nRaid Devices : 2
\nTotal Devices : 1
\nPersistence : Superblock is persistent<\/p>\n
\nState : clean, degraded
\nActive Devices : 1
\nWorking Devices : 1
\nFailed Devices : 0
\nSpare Devices : 0<\/p>\n
\nUUID : eccabf13:879f4196:1c47de11:3059e0b8
\nEvents : 6<\/p>\n
\n0 7 1 0 active sync \/dev\/loop1
\n1 0 0 1 removed
\n<\/code>
\nIt seems that you can’t remove the “missing” disk from the array even with
\n
\nmdadm \/dev\/md2 -r detached
\n<\/code>
\nI eventually found the solution to this problem. It seems (counter-intuitively) that to remove a device from the array you have to “grow” that array as follows:
\n
\nmdadm \/dev\/md2 --grow --force --raid-devices=1
\n<\/code>
\nThis resulted in the missing \/ removed \/ non-existent device being removed from the array and it being considered clean:
\n
\nmdadm -D \/dev\/md2
\n\/dev\/md2:
\nVersion : 1.2
\nCreation Time : Fri Jan 16 21:24:44 2015
\nRaid Level : raid1
\nArray Size : 32704 (31.94 MiB 33.49 MB)
\nUsed Dev Size : 32704 (31.94 MiB 33.49 MB)
\nRaid Devices : 1
\nTotal Devices : 1
\nPersistence : Superblock is persistent<\/p>\n
\nState : clean
\nActive Devices : 1
\nWorking Devices : 1
\nFailed Devices : 0
\nSpare Devices : 0<\/p>\n
\nUUID : eccabf13:879f4196:1c47de11:3059e0b8
\nEvents : 11<\/p>\n
\n0 7 1 0 active sync \/dev\/loop1
\n<\/code>
\nThis took me a while to figure out so I hope this might help someone else out there who’s trying to achieve the same thing.<\/p>\n","protected":false},"excerpt":{"rendered":"