ReadyNAS NVX problems replacing disk

I must admit I did not check the logs. Since I have a spare disk, I inserted that one and connected the "failed" one to my PC for diagnostics.
I have just noticed that /var/log/messages on the NAS has not been changed since 30 April, despite the unit being on 24/7.
At the moment, syslog only goes back 2 days and the failure was on the 10th... logrotate does not seem to be working (despite being in cron.daily). There are a syslog.1 and syslog.2 files, but they are zero-length and a few months old...

As for the new disk being smaller, hdparm reports it to have the exact same number of sectors as the other three, so I don't think that is the issue.

/var/log# hdparm -I /dev/sda | grep -i sect
        sectors/track   63      63
        CHS current addressable sectors:   16514064
        LBA    user addressable sectors:  268435455
        LBA48  user addressable sectors: 5860533168
        Logical  Sector size:                   512 bytes
        Physical Sector size:                   512 bytes
        R/W multiple sector transfer: Max = 16  Current = 0
/var/log# hdparm -I /dev/sdc | grep -i sect
        sectors/track   63      63
        CHS current addressable sectors:   16514064
        LBA    user addressable sectors:  268435455
        LBA48  user addressable sectors: 5860533168
        Logical  Sector size:                   512 bytes
        Physical Sector size:                   512 bytes
        R/W multiple sector transfer: Max = 16  Current = 0

When I explicitly inserted a smaller disk (to make sure the system was able to recognise the new disk), I got a message saying it was too small.

Netgear support recommended reinstalling the OS, so I will try that before performing a factory default.