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On Thursday, 1 April 2021 03:04:31 BST William Kenworthy wrote: |
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> On 1/4/21 12:39 am, Peter Humphrey wrote: |
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> > Hello list, |
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> > |
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> > I use gparted often, usually from SystemRescueCD, and a common task is to |
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> > move partitions to allow for one to be enlarged. I should be able to |
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> > specify all the operations in a list, but whenever I do that gparted |
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> > inserts 1MB gaps between partitions, so I have to do one at a time. Even |
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> > the latest bootable gparted CD image does the same. |
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> > |
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> > Can anyone tell me what causes this? Has it anything to do with my always |
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> > specifying partition size as a power of 8? (I'm of the old school, having |
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> > been sent on my first computer hardware course in 1972.) |
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> |
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> Forcing alignment on megabyte boundaries? - I cant find a reason, but I |
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> think I read in the past it was for efficiency with modern file systems. |
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> |
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> BillK |
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|
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Yes, 4K physical sector size and partition alignment, ubiquitous on modern |
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'Advanced Format' drives, is used by all partitioning tools these days. |
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|
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There are many references in the interwebs, but in summary modern AF spinning |
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drives have 4096 byte physical sector size with a 512 byte logical sector |
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size. To ensure alignment you could start a partition at an LBA divisible by |
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8, but since Microsoft came out with Vista's partition manager a convention of |
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1MB has been set as the starting point: |
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|
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512 * 2048 = 1,048,576 |
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|
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The 1MB (2048 logical sectors) convention for the start of a partition is used |
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to cater for various hardware and partitioning requirements, inc. different |
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RAID data stripe sizes, SSDs with different erase block sizes, etc. It |
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ensures logical-physical partition alignment to optimise performance when |
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delete/write operations take place and as long as you are not trying to |
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squeeze the very last ounce of usable space out of your terabytes of storage, |
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it achieves its stated aim. |
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|
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Parted has 3 options for aligning the start of a partition: none, minimal and |
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optimal. With 'none' it will start a partition wherever you ask it, without |
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paying heed to logical-to-physical sector alignment. With 'minimal' it will |
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shift the start/end of a partition to make sure the minimum alignment between |
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logical and physical sectors is achieved. With 'optimal' it will check if the |
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partition is aligned to a multiple of the physical block size. 'Optimal' is |
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the default. You could check/set the alignment of logical-physical sectors |
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yourself, by making sure the start of your partitions is divisible by 8, |
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instead of adopting the GParted 1MB default boundary in any cases where it is |
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not necessary. |