Abstract:
A system and method is disclosed for improved operation of a data storage device such as a hard disk drive. The overhead for data rewriting may be reduced by the periodic remapping of logical block addresses to avoid excessive adjacent track interference effects on data blocks having lower data writing rates. It may employ the indirection system to remap data “hot spots” to new locations neighboring on spare data blocks. In circumstances where it is not possible to write data next to spare data blocks, the active LBA may be periodically moved after a predefined number of write operations.

Description:
TECHNICAL FIELD 
     The present invention relates to data storage devices and in particular to data storage devices having physical data storage locations in close proximity with widely differing rates of data writing. 
     BACKGROUND 
     Data storage devices employ rotating data storage media such as hard disk drives. In a hard drive, data is written to the disk medium using a write head which generates a high localized magnetic field which aligns magnetic domains within the disk in one of two directions. In some cases, the magnetization direction is up or down relative to the plane of the disk (perpendicular magnetic recording, or PMR). In other cases, the magnetization direction is within the plane of the disk. In all cases, this data may then be read-out with a read head. The write and read heads are typically integrated within a single assembly. To achieve steadily increasing data storage densities (typically measured in bits/inch 2 ), which are now achieving levels near 10 12  bits/in 2 , the sizes of magnetic regions storing individual bits have been reduced to nm levels. 
     To achieve these increasing data storage densities, the dimensions (widths) of data tracks are being steadily decreased and the track-to-track spacings also reduced correspondingly, with the result that magnetic interference effects between neighboring tracks (adjacent track interference, ATI), and nearby tracks (far track interference, FTI) are becoming an increasing problem for the maintenance of data integrity. The current solution to this problem is to monitor the total number of writes on any given track and in idle time (i.e., in periods during which the host computer is not transmitting read or write commands to the HDD), execute a background media scan. During the background media scan, lower levels for correction (i.e., fewer error-correction code bits) are used—if the track can be read but is compromised, it is refreshed (i.e., the same data is rewritten into that same physical location on the disk medium). The time required for these data readout and rewriting operations may affect the overall performance of the HDD and is undesirable. 
     Thus it would be advantageous in a data storage system to provide a method for improved control of ATI and FTI effects with reduced overhead on HDD operation, thereby improving the overall performance of the HDD. 
     It would also be advantageous to provide a method for avoiding ATI and FTI effects on data blocks, thereby reducing or eliminating the need to rewrite the same data into these data blocks, with the corresponding overhead on HDD operation. 
     A further advantage would be to provide a method for remapping logical block addresses (LBAs) from one physical data location to another physical data location to effect a reduction in “hot spots” on the disk storage medium at which very high and continuing rates of data writing are occurring. 
     SUMMARY 
     Some embodiments provide methods for improved data storage (reading and writing) in a hard disk drive or other data storage device having data storage locations in close proximity to each other and with widely differing rates of data writing. The close proximity of these storage locations may induce magnetic interference effects (adjacent track interference, ATI, or far track interference, FTI), causing reductions in the magnetization of data bits, and consequently a need to use more error correction code bits during data readout. When increased numbers of error bits are required, the data decoding algorithm will be slower, leading to a reduction in HDD readout performance. 
     Other embodiments provide a method for improved control of ATI and FTI effects with reduced overhead on HDD operation, thereby improving the overall performance of the HDD. 
     Some embodiments provide a method for avoiding, or substantially reducing, ATI and FTI effects on data blocks, thereby reducing or eliminating the need to rewrite the same data into these data blocks, with the corresponding overhead on HDD operation. 
     Still other embodiments provide a method for remapping logical block addresses (LBAs) from one physical data location to another physical data location to effect a reduction in “hot spots” on the disk storage medium at which very high and continuing rates of data writing are occurring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an embodiment of a data storage system; 
         FIG. 2  is a schematic diagram of a writing process on a hard disk drive not embodying the present invention, illustrating the partial erasing of data due to adjacent track interference (ATI); 
         FIG. 3  is a schematic diagram of an improved writing process according to an embodiment of the invention with smaller data blocks; 
         FIG. 4  is a schematic diagram of an improved writing process according to an embodiment of the invention with smaller data blocks and double-sided ATI squeeze; 
         FIG. 5A  is a schematic diagram of a writing process in the absence of the present invention showing pre-existing data; 
         FIG. 5B  is a schematic diagram of a writing process in the absence of the present invention showing ATI effects on the pre-existing data; 
         FIG. 6  is a schematic diagram of an improved writing process according to an embodiment of the invention showing pre-existing data; 
         FIG. 7  is a schematic diagram of an improved writing process according to an embodiment of the present invention showing minimized ATI effects on the pre-existing data; 
         FIG. 8  is a schematic diagram of the improved writing process from  FIG. 7  showing minimized ATI effects on the pre-existing data; 
         FIG. 9  is a schematic diagram of the improved writing process from  FIG. 8  showing minimized ATI effects on the pre-existing data. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments can provide one or more advantages over previous methods for reducing the loss of data due to adjacent track interference (ATI). Some benefits may also be utilized to reduce the effects of far track interference (FTI). Not all embodiments may provide all the benefits. The embodiments will be described with respect to these benefits, but these embodiments are not intended to be limiting. Various modifications, alternatives, and equivalents fall within the spirit and scope of the embodiments herein and as defined in the claims. 
     Data Storage System 
       FIG. 1  is a schematic diagram of an embodiment of a data storage system  100 . System  100  includes a host computer  102 , a storage device  104 , such as a hard disk drive, and an interface  106  between the host computer  102  and the storage device  104 . Host computer  102  includes a processor  108 , a host operating system (OS)  110 , and control code  112 . The storage device or hard disk drive  104  includes controller  114  coupled to a data channel  116 . The storage device  104  includes an arm  118  carrying a read/write head including a read element  120  and a write element  122 . 
     In operation, host operating system  110  in host computer  102  sends commands to storage device  104 . In response to these commands, storage device  104  performs requested functions such as reading, writing, and erasing data, on disk surface  124 . Controller  114  causes write element  122  to record magnetic patterns of data on a writable surface of disk  124  in tracks  128 . The controller  114  positions the read head  120  and write head  122  over the recordable or writable surface  124  of disk  126  by locking a servo loop to predetermined servo positioning burst patterns, typically located in servo spokes or zones. The predetermined servo positioning pattern may include a preamble field, a servo sync-mark (SSM) field, a track/sector identification (ID) field, a plurality of position error signal (PES) fields, and a plurality of repeatable run out (RRO) fields following the burst fields. 
     In accordance with some embodiments of the invention, system  100  includes a cache memory  130 , for example, implemented with one or more of: a flash memory, a dynamic random access memory (DRAM), or a static random access memory (SRAM). 
     System  100  including the host computer  102  and the storage device or hard disk drive  104  is shown in simplified form sufficient for understanding. The illustrated host computer  102  together with the storage device or hard disk drive  104  is not intended to imply architectural or functional limitations. The present invention may be used with various hardware implementations and systems and various other internal hardware devices. 
     Notation in the Schematic Diagrams of  FIGS. 2 Through 9   
       FIGS. 2 through 9  are schematic diagrams of various writing processes both in the absence and the presence of embodiments of the present invention. A standard notation has been employed in these figures to facilitate the understanding of the various advantages of data writing processes, and how these improved writing processes differ from previously-employed writing processes. In  FIGS. 2-9 , data storage tracks on a hard drive data storage device are represented by horizontal rectangles, such as tracks  201 ,  202  and  203  in  FIG. 2 , or tracks  601 - 613  in  FIGS. 6-9 . At the far left of these track representation rectangles, track numbers, such as “1” for track  201 , and “2” for track  202  in  FIG. 2 , are shown. In current hard disk drives, the numbers of tracks may range up into the hundreds of thousands (e.g., 300,000), wherein each track may comprise at least hundreds of sectors (in some cases up to 1000), and wherein each sector may contain up to 4 kB of data, or more. Details of the numbers of tracks, sectors, and bytes within sectors are not part of the present invention. In  FIGS. 2-4 , smaller data blocks are shown as smaller rectangles within the tracks—for example data block  210  in track  201  in  FIG. 2 . In  FIGS. 5A-9 , larger data blocks are shown as larger rectangles within the tracks—for example data block  511  in track  501  in  FIG. 5A . If a data block contains data, either written currently (i.e., within the time period represented by the figure) or written previously, then this data block will be shown shaded. The darkness of the shading represents the “strength”, or degree of magnetization, of the data bits within that data block—so, for example, in  FIG. 5B , data blocks  503  and  505  are currently being written and thus the data is “strong” so the shading of blocks  503  and  505  is darker. In comparison, data block  564  represents data that has been partially erased due to double-sided adjacent track interference (ATI) arising from the writing of neighboring data blocks  503  and  505 , and thus the shading of block  564  is lighter. When data is being currently written into a data block, that block is shown with a darker outline—for example, block  210  in  FIG. 2 , or block  563  in  FIG. 5B . 
     Blocks containing previously-stored data contain the word “Data”. Blocks currently being written also contain data, but the word “Write” is used instead to indicate that this data is being written within the time period represented by that figure, and was not there before the time period represented by the figure. If a block is being written, this indicates that the indirection system has mapped that physical location (track and sector, or groups of sectors) to a logical block address (LBA). Spare data blocks are not mapped to an LBA and thus cannot receive written data. If a data block (large or small) contains the abbreviation “ATI” this signifies that it is either currently experiencing some degree of adjacent track interference (in which case the data block may also contain the word “Current”), or that this data block had previously experienced some ATI effects (in which case the data block may also contain the word “Previous”). Depending on the number of ATI events that the data has encountered, the degree of loss in signal strength may range from negligible to being serious enough to result in the loss of some or all of the data stored in that data block (i.e., even with complex error-correction code (ECC) processes employing all the error bits, the data still cannot fully be recovered). In all cases, the degree of loss in signal strength may be characterized by the number of error correction bits required for the data read-out process. In other words, “strong” data (i.e., data which has experienced minimal or no ATI) may require only eight ECC bits, whereas degraded (“weak”) data may require the use of 12, 16, or even more ECC bits. The disadvantage in reading “weak” data is that the read-out process may be substantially slowed down by the need for higher levels of error correction, thereby reducing the data read-out rate of the HDD. Within a data block, the abbreviation “UI” stands for “unimportant”, and is always used in conjunction with the abbreviation “ATI” (see above). ATI is only “unimportant” when there is no data within a data block—adjacent track interference cannot degrade data if there is no data to degrade. Data blocks denoted “Spare” do not currently contain any user data—this does not imply that they have not been previously-written; it only indicates that whatever data had ever been written in that data block has subsequently already been rewritten into another data block, possibly according to methods of the present invention. When the indirection system moves data out of a first block to a second block, this corresponds to a remapping of the LBA from the first block to the second block. 
     Within some data blocks, a notation such as “×10” or “×1000” is shown. For data blocks also containing “Write”, “×10” would be the number of data writing cycles which occurred during the time period represented by that particular figure—see data block  210  in  FIG. 2 . For data blocks also containing “Data”, “×10” would represent the number of erasing ATI events which have affected the data within that data block—as for data block  212  in  FIG. 2 . In some figures, arrows indicate the flow of data, i.e., how a particular Logical Block Address (LBA) is remapped to different physical addresses (Data Blocks) according to embodiments. 
     Data blocks have numeric labels (such as data block  210  in the upper left of  FIG. 2 ) which indicate three things: (1) the physical location (i.e., the track, and the sector or group of sectors) of the data block, (2) the specific data or absence of data already stored or currently being written, into the data block, and (3) the degree of ATI erasing which may have occurred. Thus in  FIGS. 2-9 , the same physical location of a data block within a track and sector may have differing labels as new data is written into that data block, or as that data block is affected by ATI during writing of new data into one or both neighboring data blocks. Also, even if a data block is not rewritten within a figure, if that data block encounters ATI effects resulting in a significant weakening of the data (partial demagnetization of the data bits), its data block number will also change. As an example, compare  FIGS. 7 and 8 : data blocks  752  and  754  appear in both these figures since their physical location and the data stored there do not change, whereas data block  753  in  FIG. 7  is being written a hundred times (“×100”) while that same data block in  FIG. 8  is now a spare (labelled “ 853 ”) because the logical block address which had previously been mapped to location  753  is now mapped to block  858 . Another example is the sequence of data blocks  212 ,  222 ,  232 , and  242  in  FIG. 2 , representing a data block with the same previously-written data which is progressively weakened by ATI effects from the writing in data blocks  210  to  240 . 
     ATI Problem with Fixed Writes for Smaller Data Blocks 
       FIG. 2  is a schematic diagram  200  of a writing process on a hard disk drive illustrating the partial erasing of data due to adjacent track interference (ATI) in a writing process in the absence of the present invention. Three tracks  201 ,  202  and  203  are shown repeated four times to represent a time sequence from the top to the bottom of  FIG. 2 —over this time sequence the data block initially labelled  210  has data written in it ten times (“×10”), and then at a later period data has been written into this same data block a hundred times (“×100”)—since this may not be the same data, the same data block has been relabeled “ 220 ”, thus the data block notation indicates both a physical location (track and sector or group of sectors) and also the data or absence of data already stored or currently being written there. At a still later period in time, this same data block has had data written into it a thousand times (“×1000”), and again since this may not be the same data, the data block has been relabeled “ 230 ”. Finally, at the bottom of the figure data has now been written into this same data block five thousand times (“×5000”) and the data block has been relabeled “ 240 ”). The data block neighboring this data block being written contains previously-written data which is assumed in  FIG. 2  to not be subsequently rewritten into during the time period represented by  FIG. 2 . This means that the magnetic storage medium in track  202  is subjected to repeated adjacent track interference (ATI) events without any data refresh operations being performed. As a result, it is likely that the stray magnetic fields emanating out the sides of the write head during the write operations occurring for block  210  will weaken data block  212 , and writing in data block  220  will weaken data block  222 , writing in data block  230  will weaken data block  232 , and finally writing in data block  240  will weaken data block  242 . The progressively lighter shading of data blocks  212 ,  222 ,  232 , and  242  denotes this weakening, which would be indicated by a progressive need to employ higher numbers of ECC error bits, thereby necessitating longer data readout times. By the time represented by the fourth set of tracks  201 - 203  at the bottom is reached, data block  242  may have become unreadable, with the loss of user data which was written into that data block prior to the time period represented by  FIG. 2 . Clearly this figure represents an undesirable, or even unacceptable, outcome which may be prevented with the improved writing method. Over the time period of  FIG. 2 , no reassignment of logical block addresses (LBAs) has been made, thus the data mapped to the LBA corresponding to data block  210  is also written to data blocks  220 ,  230 , and  240  resulting in a “hot spot” of excessively high levels of writing, with the resulting degradation of the data in the neighboring LBA represented by data blocks  212 ,  222 ,  232 , and  242 . Although the actual data stored in blocks  212 ,  222 ,  232 , and then  242  should be the same, the progressive weakening, and possibly even the loss of, this data is indicated by the gradually diminishing shading and by the renumbering of the data block as the magnetization is slowly reduced. 
     Reduction or Elimination of ATI Using Writing Methods According to Some Embodiments for Smaller Data Blocks 
       FIG. 3  is a schematic diagram  300  of an improved writing process according to an embodiment of the invention with smaller data blocks. Four repetitions of tracks  301 - 303  are illustrated, representing four sequential periods within the time frame of  FIG. 3 . A particular logical block address (LBA) is initially mapped to data block  311 , and then remapped to data block  322 , then remapped to data block  333 , and finally remapped to data block  345 . This sequential remapping may be executed by the indirection system according to embodiments of the invention to prevent the excessive ATI effects shown in  FIG. 2 , and thus to preserve previously-stored data in neighboring data blocks. For example, data block  314  encounters only ten ATI events before the LBA initially mapped to block  311  is remapped to block  322 . Data block  325  is a neighbor of block  322 , but since block  325  does not contain data, it is labelled “Spare ATI UI”, indicating that it is “Spare” (i.e., contains no data), it has encountered ATI effects, and these ATI effects are unimportant (“UI”) because it is spare. The LBA mapped to block  322  is remapped to block  333  after ten writes (“×10”) because the other neighboring block (not shown) to block  322  may contain data. Many data blocks in  FIG. 3  are spare, for example blocks  312 ,  313 ,  315 ,  316 ,  317 ,  321 ,  325 ,  332 ,  336 ,  342 , and  343 —this means that these physical blocks are not mapped to LBAs within at least portions of the time period represented by  FIG. 3 . There are also a number of blocks containing previously-stored data, such as blocks  314 ,  318 ,  319 , and  348 , where the data is not rewritten within the time period of  FIG. 3  (however these data blocks remain mapped to the same LBAs throughout  FIG. 3 , i.e., they are never spares within  FIG. 3 ). A data block will maintain the same label if it remains unchanged by either writing or ATI effects. So for example, spare block  317  is shown four times, top to bottom, never being written into and never being affected by ATI. Conversely, the physical address represented first by data block  312  (“Spare”—i.e., not mapped to an LBA) is then written into (after being mapped to an LBA) and relabeled  322 . Next the same physical location is unmapped from that LBA, now becoming spare data block  332 , and finally that spare data block is affected by ATI to be again relabeled  342  at the bottom of  FIG. 3  (although still unmapped to any LBA). Data block  314  is initially affected by ATI during the writing of block  311 , and then remains unaffected by any subsequent ATI events, thus maintaining the label  314  to the bottom of  FIG. 3 . 
       FIG. 4  is a schematic diagram  400  of an improved writing process according to one embodiment of the invention with smaller data blocks and double-sided ATI squeeze. Four repetitions of tracks  401 - 403  are illustrated, representing four sequential periods within the time frame of  FIG. 4 . Spare data blocks  412 ,  413 ,  415 ,  416 ,  418 ,  421 ,  425 ,  426 ,  427 ,  432 ,  433 ,  438 ,  445 , and  446 , are illustrated—these blocks represent physical locations which are not mapped to LBAs within at least portions of the time period of  FIG. 4 . Blocks  414 ,  419 ,  439 , and  444  contain previously stored data which is not re-written during the time period represented by  FIG. 4 —these blocks are mapped to the same LBAs throughout  FIG. 4 . At the top left of the figure, data is being written ten times into both blocks  411  and  417 , resulting in a “double-squeeze” of the data previously stored in block  414 —this is indicated by the notation “ATI ×20 Data”, where the “×20” shows the combined ATI data erasing effects of “×10” ATI from block  411  and “×10” ATI from block  417 . In this “double-squeeze” scenario, the rate of erasing of data due to ATI effects is doubled in block  414 . The method can prevent the loss of data in block  414  by changing the mapping of the LBA initially corresponding to block  411  to block  422  (as indicated by the arrow), and also by changing the mapping of the LBA initially corresponding to block  417  to block  423  (as indicated by the arrow). Once this remapping has occurred, possibly using an indirection system of the HDD modified according to embodiments of the invention, no further ATI events occur within block  414 —thus in the four repetitions of tracks  401 - 403 , this previously-stored data block retains the label “ 414 ” (and also retains its original LBA mapping). 
     As shown in  FIG. 4 , the LBA mapping which originally went to block  411  is first moved to block  422 , then to block  435 , and finally to block  447 , in all cases after a predetermined write count is reached—in this example, ten writes (“×10”). Similarly, the LBA mapping which originally went to block  417  is first moved to block  423 , then to block  436 , and finally to block  448 , in all cases after the predetermined write count has been reached—in this example, ten writes (“×10”). If a neighboring data block is unmapped to an LBA, it is “Spare”, such as block  415 . To indicate the ATI effects on block  415  it is subsequently relabeled “ 425 ” when data is written into neighboring block  422  (after it is changed from “Spare”  412  to “Write ×10”  422 )—this shows that the block numbering may change to indicate ATI effects on a block not containing data, even though these ATI effects are unimportant due to the lack of stored data. 
     An interesting example is block  444 , where the data has not been rewritten throughout  FIG. 4 , however three different ATI events affect the data stored in this same physical data block (with the same LBA mapping). At the top of  FIG. 4 , two ATI events combined give an “ATI ×20” condition, and then later at the bottom, a further “ATI ×10” event occurs due to the writing of data into neighboring block  447 —the result is that now block  444  has encountered thirty ATI events. Thus the method can allow for the combination of multiple ATI events by allowing a margin of error—for example if it is known that fifty ATI events are sufficient to induce some weakening of data in a block which is not rewritten, then the number of write cycles in neighboring blocks (shown here as ten) needs to be enough smaller so that with multiple write cycles, the total number of ATI events will still be below the maximum acceptable number (i.e., fifty in this example). 
     ATI Problem with Fixed Writes for Larger Data Blocks for Data Storage Systems without Embodiments 
     In some cases, data blocks containing many sequential sectors, in some cases even containing all the sectors within a track, may be mapped to a single LBA and thus written in one long write operation. Examples of this possibility are illustrated in  FIGS. 5A-9 . 
       FIG. 5A  is a schematic diagram  500  of a writing process in the absence of the invention showing pre-existing data. Spare data blocks  511 ,  513 ,  515 - 518 , and  520  are shown, along with blocks  512 ,  514  and  519  containing previously-stored data which is not rewritten during the time frame of  FIG. 5A .  FIG. 5A  represents the condition of the data storage medium prior to the write operations illustrated in  FIG. 5B . 
       FIG. 5B  is a schematic diagram  550  of a writing process illustrating the partial erasing of data due to adjacent track interference (ATI) in a writing process in the absence of the present invention. Data blocks  563  and  565  are now mapped to LBAs and experience a thousand write operations (“×1000”). As a result, the previously-written data in block  562  has been degraded substantially by single-sided ATI. Block  564  encounters twice the number of ATI erasure events (double-sided ATI) since it is between blocks  563  and  565 —this is indicated by the near elimination of shading in the figure, denoting a substantial magnetic weakening, and even possible loss of the readability, of this data. Block  566  encounters a thousand ATI events also, but since block  566  is unmapped to an LBA and thus is “Spare” and without data, the thousand ATI events that block  566  is exposed to are unimportant. Blocks  517 - 520 , which are farther away from tracks  563  and  565  are unaffected by the write operations illustrated here—this assumes less importance of far track interference (FTI), which may affect data stored in tracks as far as 30 tracks on either side of the track being written into. Embodiments of the method of the present invention may be used to correct for FTI as well as ATI. 
     Reduction or Elimination of ATI Using Writing Methods for Larger Data Blocks 
       FIG. 6  is a schematic diagram  600  of an improved writing process according to embodiments of the present invention showing pre-existing data. Spare data blocks  651 ,  653 , and  655 - 662  are shown, along with blocks  652 ,  654  and  663  which contain previously-stored data which is not rewritten during the time frame of  FIG. 6 .  FIG. 6  represents the condition of the data storage medium prior to the write operations illustrated in  FIGS. 7-9 . 
       FIGS. 7-9  are time-sequential schematic diagrams  700 ,  800 , and  900 , respectively, of an improved writing process according to embodiments of the present invention showing no loss of pre-existing data due to ATI effects. 
       FIG. 7  shows “Spare” data blocks  651 ,  756 , and  657 - 662 , as well as blocks  752 ,  754  and  663  containing previously-stored data which is not rewritten within the time period represented by  FIG. 7 . Data blocks  753  and  755  are both written a hundred times (“×100”) within the time period of  FIG. 7 , inducing partial ATI erasing of the data in block  752 . For block  752 , this ATI effect is “single-sided”, since the other neighboring block to block  752 , i.e. block  651 , is not being written. Block  754 , however, experiences twice as much ATI (double-sided ATI) since both its neighboring blocks  753  and  755  are being written. However, by limiting the total number of writes in blocks  753  and  755  to a hundred cycles, the degree of ATI erasing in block  754  may still be kept to acceptable levels, i.e., to levels which do not induce the need for significantly higher levels of ECC error bit use. Block  756  also has single-sided ATI effects due to the writing of block  755 , however since there is no prewritten data in spare block  756  (i.e., it has not been mapped to an LBA by the indirection system), this ATI is unimportant as shown. None of the other data blocks in  FIG. 7  are affected by ATI during the time period of  FIG. 7 . 
       FIG. 8  is a schematic diagram  800  of the improved writing process of  FIG. 7  showing no loss of pre-existing data due to ATI effects at a later time period than the time period illustrated in  FIG. 7 . After the hundred writes into blocks  753  and  755  illustrated in  FIG. 7 , the indirection system has remapped the LBAs previously associated with blocks  753  and  755  to data blocks  858  and  859 , respectively, as shown. Thus blocks  752  and  754  no longer experience ATI erasing and remain unaffected, thus retaining the same block labels,  752  and  754 , through the remainder of  FIG. 8 . The indirection system in this example was able to locate two spare blocks in  FIG. 7 —blocks  658  and  659  which neighbor on other spare blocks (blocks  657  and  660 , respectively). Therefore data writing into blocks  858  and  859  in  FIG. 8  will not induce the ATI erasure of any prewritten data, unlike the situation in  FIG. 7 . Although  FIG. 8  shows the indirection system limiting the number of writes to blocks  858  and  859  to a hundred write cycles, this is less important or even unnecessary in this case. Note that ATI effects from the writing of block  858  on block  859 , and the similar ATI effects from the writing of block  859  on block  858 , are not significant since both blocks  858  and  859  are being repeatedly rewritten (i.e., the LBAs which were mapped to these two blocks are receiving repeated write commands). 
       FIG. 9  is a schematic diagram  900  of the improved writing process of  FIG. 8  showing no loss of pre-existing data due to ATI effects at a later time period than the time period illustrated in  FIG. 8 . After the hundred writes into blocks  858  and  859  illustrated in  FIG. 8 , the indirection system has remapped the LBAs previously associated with blocks  858  and  859  to data blocks  960  and  961 , respectively, as shown. As for  FIG. 8 , the indirection system in this example was able to locate two spare blocks in  FIG. 8 —blocks  860  and  861  which neighbor on blocks which are either already spare (i.e., block  662 ) or which will become spare after remapping of their associated LBAs (i.e., block  859 ). Therefore data writing into blocks  960  and  961  will also not induce the ATI erasure of any prewritten data, as was the case in  FIG. 8 , but not in  FIG. 7 . Thus although  FIG. 9  shows the indirection system limiting the number of writes to blocks  960  and  961  to a hundred write cycles, this is less important or even unnecessary in this case. Note that ATI effects from the writing of block  960  on block  961 , and the similar ATI effects from the writing of block  961  on block  960 , are not significant since both blocks  960  and  961  are being repeatedly rewritten (i.e., the LBAs which were mapped to these two blocks are receiving repeated write commands). 
     Implementation of a Method 
     The method may be implemented using the pre-existing indirection system of the HDD. The indirection system is used to map logical block addresses (LBAs) to physical addresses (tracks and sector numbers) on the physical disk surface (e.g., surface  124  in  FIG. 1 ). The method can employ a write counter for each data block to keep track of the number of write cycles at that physical location. Note that the method may concern the physical locations of data blocks, since ATI effects occur between neighboring physical data blocks (on neighboring tracks), and are independent of the LBA addresses. However the method can employ remapping of LBAs to effect the reduction or elimination of ATI effects between physical data blocks. 
     Alternative Embodiments 
     Although embodiments have been described in the context of hard disk drives, it should be understood that various changes, substitutions and alterations can be made. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, or composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of embodiments, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.