Whitepaper | May 2008
Critical data, like file system related information, license data, and potential content data bases – all meta- data – ought to reside in a zone with full error recovery procedures (ERP).
Audio data, which is rather sensitive to so called glitches, ought to be treated with medium error recovery, still guaranteeing the fairly low data rates typically involved.
Standard definition video content might be best served by applying short ERP before the HDD needs to respond, while high definition content might require even tighter limits to be set.
Read Continuous for 3.5-inch CinemaStar
‘ R e a d C o n t i n u o u s ’ m o d e i s c o n t r o l l e d b y a c o n fi g u r a t i o n fl a g , w h i c h d e t e r m i n e s t h e H D D ’ s e r r o r r e c o v e r behavior. In ‘Read Continuous’ mode (flag = 1) the drive will attempt to read exact data from all sectors ad- dressed by a particular command within the defined time limit. Should individual sectors require exces- sive time to recover exact data, a best eort will be made to recover all stable data bits while applying only ECC-based correction to the remaining bits. ECC stands for Error Correction Codes generated by the hard disk drive for every data sector upon the original write operation for later use in read operation. If no time limit has been set, the ‘Read Continuous’ flag triggers the drive to deliver ECC corrected data without delay. y
In the standard operating mode (flag = 0), the drive will apply the defined command turn around time limit only. Should the full recovery of all sectors not be possible within the limit, the associated command is aborted and an error flag is set by the drive, leaving it to the host to determine whether to retry the last com- mand or to skip to the next frames in the case of a video sequence.
The AV-Zoning and Read Continuous features are not yet implemented in the 2.5-inch CinemaStar C5K320.
Media Maintenance for 2.5- & 3.5-inch CinemaStar
HDD design was originally driven by IT-type applications and associated data access patterns to be execut- ed. In order to make these drives suitable for continuous streaming operations, potentially working around the clock, HGST has developed a number of functions to ensure that individual components don’t wear out prematurely.
One critical area is the protective lubrication layer on the media surface that could get displaced if a data head was flying over the same tracks continuously, as a result of repeated or low data rate playback, for instance. CinemaStar drives will therefore utilize the time between access commands to actively reposition their data heads.
Over an extended period, frequent AV content re-fresh operations, as we find in Set Top Boxes (STB) operating 24x7 can have a negative impact on static data residing right next to those tracks recording movie
after movie. HGST studied this phenomenon carefully before engaging with the world’s set top box makers and has implemented protective measures, keeping static data safe beyond hundreds of thousands of recordings.
For maximum protection during transport and idle modes, HGST equips all drives with a load/unload mechanism, moving the heads away from the data carrying medium. This prevents mechanical contact and avoids the associated damage to the media. CinemaStar drives employ the same mechanism with modified operating algorithms to prevent excessive sound generation and potential wear-out from unnecessary head unload operations, which could otherwise be triggered by low activity tasks, e.g, a low bandwidth audio down-load.
CE Features of the Second Generation CinemaStar Hard Disk Drives