Having just passed 1PB written, we decided to check that all was still well with the SSD by powering it off for 36 hours. On restarting the server, we checked that the SSD was still visible and then tried reading the huge static file we had been using for the last stage of testing:
# dd if=/data/static of=/dev/null bs=1G iflag=direct 810+0 records in 810+0 records out 869730877440 bytes (870 GB) copied, 3033.31 s, 287 MB/s
No errors were reported, and performance was the same as earlier - limited by the SATA2 connection currently in use. SMART reports that the flash is only 18% worn - 82% still to go, so the tests are going to be running for a while yet!