We have a very old Dell desktop machine that has been running CentOS 6 for the past five years.  It received a new, 1 TB disk and additional memory before the OS installation.  It has been the primary Linux machine in our smallest and most remote field office.  It has been updated at least once a week and has all current dates installed.

Boot-up this morning lasted about six times as long as usual. Disk access, as indicated by the disk activity light, is almost continuous and for extended periods of time when ever something is done that requires the disk.  Everything observed happens whether or not the machine is connected to our network. All of our files appear to be accessible if one is patient.

One theory put forward is that some application is running that uses up CPU and disk bandwidth.  Another theory is that there are disk errors, mostly corrected by EDCS features. We do not see any rogue applications and error logs show no disk issues.

This is a mysterious issue that we hope to circumvent by putting a new disk and installing CentOS 7 from DVD.  Our hope is that the current disk can be mounted externally on the new CentOS system using a USB to SATA adapter and that data can be moved off of the old disk. Advice regarding this issue and any possible diagnostic methods will be greatly appreciated.

df -k output:
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Filesystem        1K-blocks      Used Available Use% Mounted on
/dev/mapper/vg_delle520-lv_root
51475068  12110896  36742732  25% /
tmpfs               1928152       176   1927976   1% /dev/shm
/dev/sda1            487652    211073    250979  46% /boot
/dev/mapper/vg_delle520-lv_home
905124888 246856176 612284356  29% /home
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