I tried changing a column on a table with a few million records, changing a varchar column length from 100 to 250. After more than one and a half hours of execution time, whereupon monitoring the connection, it was almost all the time with a SUSPENDED state and PAGEIOLATCH_EX wait type, with very short intervals where the state changed to RUNNING.
I couldn't tell if it took that long due to an index being recomputed, disk being slow (didn't seem like it), or this was simply the expected behavior. Nor could I tell how long the task would take, so I just gave up and stopped the process.
Is there a way to know beforehand if there's something to be done for the task to run on a shorter time interval, or at least to know how much is left to do when the task is running?
As suggested by @J.D, I've run a benchmark on the SQL server SSD and I got some below average results, at least less than I would expect from an SSD imho. Here are the results. So maybe it has something to to with the performance: