We currently have two servers with SATA disks. The box load on the box every so often jumps. We see a direct correlation between the IO wait and the system usage going up. When ever the IO is high the system CPU usage jumps as well. The server has hardware raid with the drive showing as /dev/sda. We re running CentOS. We want to install two SSD's in a raid 1 as well, boot from a USB key and then use dd to copy from the SATA disks over to the SSD's. Once we copy everything over we will remove the original array and leave just the second. Will this work? How does Linux assign which disk is /dev/sda or /dev/sdb?
Switching disks
centos;hard disk;dd
As you have the LVM partition I would recommend you the following steps:First switch the fstab and grub configuration to use UUIDs for /boot volume the system uses.Next, attach the SSD device, boot the system from the RAID and partition the SSD to have two partitions: for a new /boot volume and a new LVM PV.Then add that new PV to existing VG and migrate all LVs to an SSD's PV (check with man lvm for all necessary commands).After migration is done, remove the RAID's PV from a Volume GroupThen copy with tar or rsync the content of /boot file system to the new location (the /boot partition on SSD) preserving ACLs and SE contexts, adjust the kernel settings in the grub configuration and install grub on SSD.