zfs need not store 2 copies of all metadata
From Matt Ahrens's bug report at Delphix:
Add a new zfs property, "redundant_metadata" which can have values "all" or "most". The default will be "all", which is the current behavior. Setting to "most" will cause us to only store 1 copy of level-1 indirect blocks of user data files.
From the new man-page entry:
redundant_metadata=all | most Controls what types of metadata are stored redundantly. ZFS stores an extra copy of metadata, so that if a sin- gle block is corrupted, the amount of user data lost is limited. This extra copy is in addition to any redun- dancy provided at the pool level (e.g. by mirroring or RAID-Z), and is in addition to an extra copy specified by the copies property (up to a total of 3 copies). For example if the pool is mirrored, copies=2, and redundant_metadata=most, then ZFS stores 6 copies of most metadata, and 4 copies of data and some metadata. When set to all, ZFS stores an extra copy of all meta- data. If a single on-disk block is corrupt, at worst a single block of user data (which is recordsize bytes long) can be lost. When set to most, ZFS stores an extra copy of most types of metadata. This can improve performance of random writes, because less metadata must be written. In prac- tice, at worst about 100 blocks (of recordsize bytes each) of user data can be lost if a single on-disk block is corrupt. The exact behavior of which metadata blocks are stored redundantly may change in future releases. The default value is all.
Updated by Rich Lowe about 7 years ago
I'd missed snapshot-specific properties when I looked, my apologies.
I was looking at both 'zfs get all' and 'zpool get all', the latter has underscores in feature names, but the former has none at all. I was just suggesting the same name with the underscore removed, which seems to be no more unwieldy than 'casesensitivity' or 'logicalreferenced' or 'usedbydatasets'. It's not a big deal, I was just shooting for consistency, which as you point out, we already lack.
Updated by Electric Monk about 6 years ago
- Status changed from In Progress to Closed
commit edf345e6b8342e8627ec20ce821a977a62cee19d Author: Matthew Ahrens <firstname.lastname@example.org> Date: 2014-05-23T16:21:07.000Z 3835 zfs need not store 2 copies of all metadata Reviewed by: George Wilson <email@example.com> Reviewed by: Adam Leventhal <firstname.lastname@example.org> Reviewed by: Dan McDonald <email@example.com> Approved by: Richard Lowe <firstname.lastname@example.org>