I have a CentOS 6 box running RAID1. It had two 500 GB hard drives, but they were old and slow so I asked my provider to upgrade to new larger ones (1 GB each). The provider did this by shutting down the computer, replacing one drive, letting the RAID sync the discs, and then replacing the other and syncing again.
As a result, the filesystem is still 500 GB, even though the drives are 1 TB each.
What's the best way to make the new space available? Ideally, I would prefer to resize a partition instead of adding one, but I've been told that can be dangerous.
This is what fdisk shows for /dev/sda (/dev/sdb is similar). /dev/sda4 and /dev/sdb4 are new, unused partitions.
/dev/sda1 * 2048 526335 262144 fd Linux raid autodetect
/dev/sda2 526336 8914943 4194304 fd Linux raid autodetect
/dev/sda3 8914944 111314943 51200000 fd Linux raid autodetect
/dev/sda4 111314944 976773167 432729112 5 Extended
/dev/sda5 111316992 119705599 4194304 82 Linux swap / Solaris
/dev/sda6 119707648 976773119 428532736 fd Linux raid autodetect
If you have remote console/KVMoIP, then you could mount a linux rescue disc of some sort then resize the software raid 1 array using mdadm. It could be dangerous in that if the server crashed or shut off, your partitions might be broken. Have backups if you plan to go this route.
Otherwise, just format the "extra" 500GB into another usable partition.