Re: RFC: raid with a variable stripe size

[Goffredo Baroncelli <kreijack@inwind.it>]

On 2016-11-29 01:48, Qu Wenruo wrote:
> For example, if sectorsize is 64K, and we make stripe len to 32K, and use 3 disc RAID5, we can avoid such write hole problem.
> Withouth modification to extent/chunk allocator.
> 
> And I'd prefer to make stripe len mkfs time parameter, not possible to modify after mkfs. To make things easy.

This is like the Zygo idea: make the sector_size = (ndisk-1) * strpe_len... If this could be possible to implement per BG basis you answered the Zygo question. Of course when the number of the disk increases the disk space wasting increases too. But for small RAID5/6 (4/5 disk) it could be an acceptable trade-off.

Anyway on the basis that SSD is the future of storage, I think that our thoughts about how avoid a RMW cycle don't make sense. The SSD firmware remaps sectors, so what we think as "simple write" may hide a RMW because the erase sector are bigger than the disk sector (4k ?).

> 
> Thanks,
> Qu


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