Re: Avoiding BRTFS RAID5 write hole

Goffredo Baroncelli
2019-11-13T19:34:26Z

On 12/11/2019 23.27, Hubert Tonneau wrote:
> Goffredo Baroncelli wrote:
>>
>> Instead I would like to investigate the idea of COW-ing the stripe: instead of updating the stripe on place, why not write the new stripe in another place and then update the data extent to point to the new data ? Of course would work only for the data and not for the metadata.
>
> We are saying the same.

The main difference is that my solution is permanent. The new data in new place is valid as the old one. In your idea, you talk about a secondary step of updating the stripe.

> What I am suggesting is to write it as RAID1 instead of RAID5, so that if it's changed a lot of times, you pay only once.
I am not sure to understand what are you saying. Could you elaborate ?

>
> The background process would then turn it back to RAID5 at a later point.
> Adjusting how aggressively this background process works enables to adjust the extra write cost versus saved disk space compromise.
>

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