Re: Recommended filesystem for RAID 6

[Chris Murphy <lists@colorremedies.com>]

On Tue, Aug 11, 2020 at 1:47 PM Wols Lists <antlists@youngman.org.uk> wrote:
>
> On 11/08/20 20:19, Michael Fritscher wrote:
> > Hi,
> >
> > if you really want to use these tiny 2 TB HDDs - yes, RAID 6 (2x - the
> > second for the backup system on a physically different location) is a
> > good choice.
> >
> > But: If you can, buy some 8-12 TB HDDs and forget the old rusty tiny
> > HDDs. You'll save a lot at the system - and power.
> >
> I'm looking at one of these ...
> https://www.amazon.co.uk/Seagate-ST8000DM004-Barracuda-internal-Silver/dp/B075WYBQXJ/ref=pd_ybh_a_8?_encoding=UTF8&psc=1&refRID=WF1CTS2K9RWY96D1RENJ
>
> Note that it IS a shingled drive, so fine for backup, much less so for
> anything else.

How can you tell? From the spec, I can't find anything that indicates
it. Let alone which of three varieties it is.
https://www.seagate.com/www-content/product-content/barracuda-fam/barracuda-new/en-us/docs/100805918d.pdf

>I'm not sure whether btrfs would be a good choice or not ...

Btrfs tries to write sequentially, both data and metadata, which
favors SMR drives.

For device managed SMR there are some likely optimizations to help
avoid random writes. Top on that list is for the workload to avoid
fsync. And also using mount options: longer commit time, notreelog,
space_cache v2, and nossd. If the drive reports rotational in sysfs,
then nossd is used by default. Space cache v2 is slated to become the
default soon.

For host managed SMR there are significant requirements. Including a
log structured super block.
https://lwn.net/Articles/806327/

Quite a lot of preparatory work has been happening before this series
lands in mainline. For other file systems, I'm not sure, but my guess
is using dm-zoned, basically making non-sequential writes from XFS and
ext4 into sequential writes and ensuring the various alignment
requirements.


-- 
Chris Murphy