Re: RAID 5, 10 modern post 2020 drives, slow speeds

[Roman Mamedov <rm@romanrm.net>]

On Fri, 7 Mar 2025 14:42:24 -0600
Roger Heflin <rogerheflin@gmail.com> wrote:

> I put an external bitmap on a raid1 SSD and that seemed to speed up my
> writes.  I am not sure if external bitmaps will continue to be
> supported as I have seen notes that I don't exactly understand for
> external bitmaps, and I have to reapply the external bitmap on each
> reboot for my arrays which has some data loss risks in a crash case
> with a dirty bitmap.
> 
> This is the command I used to set it up.
> mdadm --grow --force --bitmap=/mdraid-bitmaps/md15-bitmap.img /dev/md15

In this case the result cited seems to have shown the bitmap is not the issue.

I remember seeing patches or talks to remove external bitmap support, too.

In my experience the internal bitmap with a large enough chunk size does not
slow down the write speed that much. Try a chunk size of 256M. Not sure how
high it's worth going before the benefits diminish.

-- 
With respect,
Roman