RAID-Z wasted space - asize roundups to nparity +1

[Olivier Smedts]

2013/1/29 Adam Nowacki <nowakpl at platinum.linux.pl>:
> This brings another issue - recordsize capped at 128KiB. We are using the
> pool for off-line storage of large files (from 50MB to 20GB). Files are
> stored and read sequentially as a whole. With 12 disks in RAID-Z2, 4KiB
> sectors, 128KiB record size and the padding above 9.4% of disk space goes
> completely unused - one whole disk.
>
> Increasing recordsize cap seems trivial enough. On-disk structures and
> kernel code support it already - a single of code had to be changed (#define
> SPA_MAXBLOCKSHIFT - from 17 to 20) to support 1MiB recordsizes. This of
> course breaks compatibility with any other system without this modification.
> With Suns cooperation this could be handled in safe and compatible manner
> via pool version upgrade. Recordsize of 128KiB would remain the default but
> anyone could increase it with zfs set.

One MB blocksize is already implemented by Oracle with zpool version 32.

-- 
Olivier Smedts                                                 _
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