The basic reason is that we aren't claiming the IBM drives are "AV" drives is because IBM doesn't claim it. When you get right down to it, there is no spec for what makes a drive AV but it is generally assumed that it means that the drive has a certain guaranteed minimum sustained transfer rate.
All hard drives have periodic actions which kick in at various times to do certain maintenance-like things, like compensating for temperature changes. These periodic activities are typically scheduled for idle periods where the drive hasn't received a request for a certain amount of time (usually a second or longer). This will keep them from interrupting a video capture or playback. There are some periodic activities however that may interrupt a read or write request. It is these activities that keep a drive from maintaining a minimum transfer rate.
The Micropolis AV drives were the first drives to prevent any periodic activity from interrupting the handling of a read or write and also to reduce the duration of any of the periodic activities. This second change was done so that, even if a drive hasn't received a request for 5 seconds, if the first request happens just after a periodic function has started, the command would still be completed within a certain reasonable time.
The IBM drives have a lot of different periodic activities but only one of them will interrupt a stream of commands - the Predictive Failure Analysis (PFA) function. PFA is a very obscure attempt at giving a possible early warning that the drive is failing. Because it is the only periodic activity that keeps the drive from maintaining a minimum transfer rate, we disable PFA during production. We have verified with the IBM engineers that this is the only drive function that keeps us from claiming AV-capability and that this doesn't add any risk or reliability issues. Even with PFA on, the drive will detect and correct any errors as readily as any drive.
We don't feel comfortable calling this an "AV" drive because IBM doesn't call it an "AV" drive. However, if you look at what AV means and if you realize that most of the true AV (video) work out there is not done on Micropolis AV drives, it is safe to say that, with PFA disabled, the IBM drives are "AV-capable."
Machines Affected: All systems using IBM 2GB or 4GB hard drives