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ED#178 : AV-Optimized Hard Disk Drives Are Safe To Use
For years, we have been debunking hard disk drive myths. Never did we expect to actually be the creator of a hard disk drive myth ourselves. Sadly, we did just that, and today, we want to kill this myth that we created. This was the myth we created :
Not For Desktop Use Unlike desktop hard disk drives, the <AV drive> is designed to skip error correction in favour of completing commands on time. This prevents a disruption of the video or audio stream due to time-consuming error correction routines at the expense of some bad data. This is great for CE-type applications like recording video and audio streams off cable or CCTV feeds. A few off-colour pixels are far less noticeable than a few missing frames. However, no one can accept bad data in a desktop or server environment. When we copy a document to a hard disk drive, we expect its content to be 100% identical to the original. If a bit is determined to be bad, we expect the hard disk drive to correct the error before writing it. It would not do if the drive simply ignores the error and writes the bad bit in order to ensure it completes the operation on time. Some unscrupulous or misinformed dealers are promoting such AV-optimized hard disk drives as "superior" versions of their desktop cousins with appropriately higher price tags. Nothing could be further from the truth. These AV-optimized hard disk drives are neither superior nor inferior to their desktop equivalents. They are designed to be used in very specific applications, and are not meant for use in desktop or server environments. |
Well, that was categorically WRONG, and we apologize for the mistake. The AV-optimized drive's ability to skip error correction is limited only to systems that specifically make use of the ATA Streaming commands.
Therefore, AV-optimized hard disk drives will NOT have data corruption issues if they are used in a desktop or server environment. They will function essentially like any other hard disk drive.
We would like to thank Tiggle and E.B.E. for first pointing this out to us.
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How Did This Happen?
The first AV-optimized hard disk drives started appearing in 2010, boasting AV-specific features like :
- full support for ATA Streaming commands
- optimized video streaming through SMART Command Transport (SCT)
- firmware optimized for write-intensive operations
- rated for higher operating temperatures
- rated for 24/7 operation
The misunderstanding stemmed from the new ATA streaming commands, particularly AV Error Recovery and Continuous Read/Write Controls. They are all features designed to prevent read / write errors from disrupting a smooth flow of video and audio streams. What we wrote about these features is true and correct - they will skip some data if it takes too long to read or write, or if the error correction process takes far too long.
However, these features are only activated if the host device (usually a CCTV system) specifically uses the ATA Streaming commands to enable these features. In a desktop or server, the ATA Streaming commands are not used. Therefore, these features would not be activated and the hard disk drive will behave like any other regular hard disk drive.
The misunderstanding was compounded when we queried Western Digital about this, and were informed that the time limit for error correction in their AV-GP drives (at that time) was preset to 100 ms, and this cannot be modified by the ATA Streaming Command Set. They are correct, of course, but if the host device does not support or use the ATA Streaming Command Set, then the time limit is irrelevant.
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So I Can Use AV-Optimized Drives In Desktops And Servers?
Technically, there's no issue in using an AV-optimized drive in any desktop or server. As far as data integrity is concerned, they are just like any regular hard disk drive. As they are (usually) rated for higher operating temperatures and non-stop operation, they may even be more reliable than regular hard disk drives.
In fact, Western Digital actually run their AV-optimized drives at a higher spindle speed than their desktop versions. Check out this comparison of the transfer rate ranges of Western Digital's AV-optimized drives versus their desktop versions :
Although Western Digital never reveals the actual spindle speed, our tests reveal that the AV-optimized drives have a higher spindle speed. The AV-GP drives are physically the same as the Caviar Green drives in this comparison, with the same number of platters, the same areal density and even the same cache size. So the only explanation for the higher raw throughput is a higher spindle speed. This was also supported by the higher thermal output of the AV-GP drives :
That said, these AV-optimized drives are optimized for write operations, specifically large writes. So their performance characteristics will be quite different from regular hard disk drives. In the next page, we have a performance comparison of two AV-optimized drives and their desktop analogues. Check it out!
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AV-Optimized Hard Disk Drives Are Safe To Use |
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Not For Desktop Use? |
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