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Masking Logical Sectors on 4K Sector Drives

IP.com Disclosure Number: IPCOM000200647D
Publication Date: 2010-Oct-22
Document File: 6 page(s) / 84K

Publishing Venue

The IP.com Prior Art Database

Abstract

Implement masking of logical sectors in Advanced Media format (4K physical sector) emulated hard disk drives so that the imaging software can mask logical sector(s) as needed to make various partitions and volumes get laid out in 4K aligned way on these drives. For emulated drives, a physical 4K sector has a layer of logical sectors on its top. Each physical sector will have a layer of 8 (512 bytes each) logical sectors on its top logically. Each logical sector has a logical bock address (LBA). The first logical sector has LBA 0. So, the first physical sector will have sector with LBA 0 -7. Along the same lines, the 8th physical sector will have sectors with LBA 56 - 63. This results in the 63rd LBA being at an offset of 512 bytes with regard to its underlying physical sector. A windows XP partition laid out per existing implementation of a backup and recovery tool such as Symantec’s BESR (which falls in line with actual layout of Windows XP on the source disk volume) could thus be misaligned by 512 bytes when laid out on 4K sector disk. If the first logical sector. i.e. Logical Block Address (LBA) 0 is masked, the new LBA for all of the subsequent sectors will be = Old LBA -1. In line with this, if the first LBA on a 4K sector disk is masked, the sector that has LBA 64 will now have LBA value = 63. In this scenario, LBA 63 will be at 0 offset with regards to its underlying sector. Now, if, for example, BESR code would layout its partitions, the new layout will be 4K aligned as BESR would still layout the first partition at 63rd LBA. BESR would also need to make sure while restoring subsequent volumes on these disks that they also get laid out on 4K boundaries. It would be possible if a few other LBAs at random locations on the disk could also be masked using a software API/interface provided by hard disk vendor. This will allow BESR to still layout partitions as per its existing layout algorithm without accounting for layout changes mentioned earlier. For example, if the next partition is to be laid out at sector that has LBA = 20000, BESR will have to make some simple calculations to figure out no of LBAs to masks. In this case the following conditions to be met will provide us number of sectors to mask. mod ((20000 + x) / 8) == 0, where x is number of LBAs to mask in total. y = x - a, where y is number of LBAs to mask now and a is number of LBAs already masked on the disk. This could result in the following implementation on HDD : a. An ability to mask logical sectors using software API / HD interface commands that can be sent though software. b. An ability to determine no of logical sectors already masked and their physical locations in the emulated layer. c. An ability to protect the area of drive so that it cannot be masked anymore. This will prevent accidental masking of used sectors. d. Removal of all of the masking and protection with a single command (when disk is to be formatted). Many new hard drives currently handle bad sector detection and their handling within HDD firmware itself. They internally maintain a list of bad sectors and implement sector remapping for all sectors following the bad sector that has been detected. Once such implementation is discussed at http://www.mjm.co.uk/sectorremapping.html A similar approach could be used for masking logical sectors. However, HDD vendors can choose to implement the masking of logical sectors in the way it fits their hardware design though. This paper refers to the idea of providing a logical sector masking in HDD itself. It needs to be implemented in the way such that the above mentioned interface requirements are met so that imaging software vendors can benefit from it.

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Masking Logical Sectors on 4K Sector Drives

Ravindra Teli

Symantec Corporation

Abstract

Implement masking of logical sectors in Advanced Media format (4K physical sector) emulated hard disk drives so that the imaging software can mask logical sector(s) as needed to make various partitions and volumes get laid out in 4K aligned way on these drives.

For emulated drives, a physical 4K sector has a layer of logical sectors on its top. Each physical sector will have a layer of 8 (512 bytes each) logical sectors on its top logically. Each logical sector has a logical bock address (LBA). The first logical sector has LBA 0. So, the first physical sector will have sector with LBA 0 -7.  Along the same lines, the 8th physical sector will have sectors with LBA 56 - 63. This results in the 63rd LBA being at an offset of 512 bytes with regard to its underlying physical sector. A windows XP partition laid out per existing implementation of a backup and recovery tool such as Symantec’s BESR (which falls in line with actual layout of Windows XP on the source disk volume) could thus be misaligned by 512 bytes when laid out on 4K sector disk. If the first logical sector. i.e. Logical Block Address (LBA) 0 is masked, the new LBA for all of the subsequent sectors will be = Old LBA -1. In line with this, if the first LBA on a 4K sector disk is masked, the sector that has LBA 64 will now have LBA value = 63. In this scenario, LBA 63 will be at 0 offset with regards to its underlying sector. Now, if, for example, BESR code would layout its partitions, the new layout will be 4K aligned as BESR would still layout the first partition at 63rd LBA. BESR would also need to make sure while restoring subsequent volumes on these disks that they also get laid out on 4K boundaries. It would be possible if a few other LBAs at random locations on the disk could also be masked using a software API/interface provided by hard disk vendor. This will allow BESR to still layout partitions as per its existing layout algorithm without accounting for layout changes mentioned earlier.  For example, if the next partition is to be laid out at sector that has LBA = 20000, BESR will have to make some simple calculations to figure out no of LBAs to masks. In this case the following conditions to be met will provide us number of sectors to mask. mod ((20000 + x) / 8) == 0, where x is number of LBAs to mask in total. y = x - a, where y is number of LBAs to mask now and a is number of LBAs already masked on the disk. This could result in the following implementation on HDD :

a. An ability to mask logical sectors using software API / HD interface commands that can be sent though software.

b. An ability to determine no of logical sectors already masked and their physical locations in the emulated layer.

c. An ability to protect the area of drive so that it cannot be masked anymore. This will prevent accidental masking of used sectors.

d. Removal of all of the masking and protection with a sing...