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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?

  • As far as i know which device is assigned sda sdb sdX is not deterministic, and that's why many of us utilize UUIDs (yet there are other options). there are many good internet sources for persistent device naming, here is just one (and a good one): wiki.archlinux.org/index.php/persistent_block_device_naming – Theophrastus Sep 16 '16 at 17:08
  • What type of partitions do you have on top of that RAID massive? – Serge Sep 16 '16 at 17:12
  • Can't seem to figure out how to do newline here. Here is the output of the sever pastebin.ca/3718909 – Dovid Bender Sep 16 '16 at 17:23
  • @DovidBender regarding formatting, you can't put newlines in a comment, but you can do much of the rest of the markdown which you can read up on here and here – Eric Renouf Sep 17 '16 at 1:24
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    It's typically better to edit the question to include new details arrising from the comments. – Stephen Harris Sep 17 '16 at 2:56
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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 Group

Then 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.

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