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Comment Re:all i want is BP-rewrite (Score 1) 297

If you move a de-duped block to defragment file X, then the same block referenced by file Y is now not in order.

That's fine. Seriously, when do you ever have a block in common between two files that are not identical copies of the whole file? Certainly not in the middle of a giant file. By nature, giant files (music, video) are compressed and essentially random. Maybe as the very last block in a file, or in a very small file, in which case out-of-order is a non-issue.

If it is in memory cache the whole concept is moot anyhow - whether it is fragmented on disk or not is irrelevant.

The hash mapping between block ID and disk location should be kept in memory. The actual data doesn't need to be.

Given that with de-dup, we are dealing with BLOCKS and not complete files, what order do you propose they are sorted in? Or are you talking about just "Defragmenting" by consolidating them all at the start of the disk, which would make more sense?

First, sorted in order of first known occurrence in a file. Then, consolodated at the start of the disk (if the data is largely static). Defragmenting free space is more important often than defragmenting files.

Comment Re:all i want is BP-rewrite (Score 1) 297

No no no no no. No.
When you want to read the actual data pointed to by the lookup table, the disk head goes to the location where the data is now, not where it was originally. Where it was originally is never stored — and never needs to be. All block IDs are looked up and converted to disk locations on-the-fly at read time, using an in-memory-cache that is mutexed to prevent corruption during background operations. And moves can be done in the background without delaying foreground tasks by copying first and then updating the table pointers.

Comment Re:all i want is BP-rewrite (Score 1) 297

ZFS can have up to 18,446,744,073,709,551,616 snapshots, and if you change the location of a block of data, you need to update it's block pointer in all of those snapshots, assuming each one points to it.

That's an incredibly naive implementation then. It would be far superior to store the ID of the block, rather than the location of the block. Then you look the location up in a table, given the ID. Then blocks can move around as needed, as a background process, without harming any data structures. This is exactly how virtual memory paging tables work. Why can't disks do this?

Comment Re:all i want is BP-rewrite (Score 1) 297

That said, defragmentation is intrinsically incompatible with deduplication, as it is not possible to have multiple files that all refer to some of same blocks all being contiguous on disk.

You don't store the address or location of a block, you store the ID of the block's unique data. When/if you need to know the location of the block, you look it up an ID-to-address table. There's absolutely nothing intrinsically incompatible between defragmentation and deduplication.

Comment Re:um (Score 1) 108

Agreed 100%. Also — and this is most important for me — the iPad has a way higher resolution (in terms of pixels per inch density) than my laptop screen has. The iPad is simply gorgeous for reading things. (iPad 3 and iPad 4)

Comment iPad Mini is too small and low resolution (Score 1, Insightful) 192

iPad Mini is a very foolish choice. It's only 768x1024. Should be a retina iPad instead, which is 1536x2048.

The 1536x2048 resolution of the iPad 3/4 is miles better than the 768x1024 resolution of the old iPad and the iPad Mini. Frankly, 768x1024 is insufficient for reading anything but pure text like novels. You need 1536x2048 for technical material or anything serious at all.

Comment Re:Either way. (Score 5, Informative) 203

You know, if you were just joking, then you should have just let it go. Now you look like you're grasping at straws to justify what you said, since any (reasonably-educated) native English speaker will be familiar with the definition of 'fraction' that he was using.

Sarten-X is 100% correct — and his original post was hilarious in my opinion. Fractions do not need to be less than 1 (or greater than -1, for that matter). Common English definitions are irrelevant here; this is a mathematical definition.

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