On Wednesday March 25, drees76@xxxxxxxxx wrote: > I picked up a SSD (30GB OCZ Vertex if you're curious) and am planning > to set up a RAID1 with it and a SATA disk with the SATA disk in > write-mostly mode along with write-behind enabled. > > So I went to test it to make sure I had all the details correct on > aligning the partition to a 128kB offset and the correct mdadm > commands to create the array in write-mostly and write-behind, but I > found that I couldn't get writes to "write-behind". Essentially all > writes would complete at the speed of the rotating disk. Reads > however worked great - they all appeared to be coming from the SSD. > > I created the array with the following command: > > mdadm --create /dev/md0 --raid-devices=2 --level=1 \ > --bitmap=internal --write-behind /dev/sdb1 --write-mostly /dev/sda1 Hmmm... try with an external bitmap stored elsewhere on the SSD. When you have bitmap=internal, bitmap updates are synchronous to all devices. Maybe that is causing the loss of speed that you see. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
