In case someone wonders in future why SW RAID5 or 10 is slow. Unless, two or more process do not write in parallel - ARRAY SPEED WILL ALWAYS BE SINGLE DRIVE LIMIT. Basically, any single user operations of storing data on the array will became as writing to single drive. In case of modern SATA HDDs, it would be 120-220MBs Only the HW RAID controllers are allegedly capable to write on more than one drive parallel thus achiving the logical/envisioned/intuitive speed. based on theory where at least two chunks are written at once to the two different drives thus doubling the writing speed as confussingly written in all RAID wikis. -------- Original Message -------- On 07/03/2025 21:47, Roman Mamedov <rm@xxxxxxxxxxx> wrote: > On Fri, 7 Mar 2025 14:42:24 -0600 > Roger Heflin <rogerheflin@xxxxxxxxx> 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 >
