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

[Steven Hartland]

----- Original Message ----- 
From: "Olivier Smedts" <olivier at gid0.org>


> 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.

Oracle is not the upstream, since they went closed source, illumos is our new
upstream.

It you want to follow the discussion see the thread titled "128K max blocksize in
zfs" on developer at lists.illumos.org.

    Regards
    Steve

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