HFS to APFS - Deduplicate Existing Files

LERsince1991

macrumors 65816
Original poster
Jul 24, 2008
1,245
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UK
As the title suggests I will convert all my HFS drives (internal and external) over to APFS, I believe this is to be a seamless process without loss of files, but will its deduplication capabilities work on existing duplicated files?

For example will it run deduplication comparison on existing files to create additional space where possible, or will it only log new copies.

Bonus question - On many files I already use hard links to avoid duplicated data, I believe these hard links will remain OK once converted?

Thanks,
 

casperes1996

macrumors 601
Jan 26, 2014
4,901
2,766
Horsens, Denmark
As the title suggests I will convert all my HFS drives (internal and external) over to APFS, I believe this is to be a seamless process without loss of files, but will its deduplication capabilities work on existing duplicated files?

For example will it run deduplication comparison on existing files to create additional space where possible, or will it only log new copies.

Bonus question - On many files I already use hard links to avoid duplicated data, I believe these hard links will remain OK once converted?

Conversion should be smooth, yes. Note though that per default Apple doesn't convert HDDs. Only disks that have an SSD element, presumably because of changes in block size or something like that, that would decrease performance on spinning platter disks.

Deduplication of existing duplicates is something I'd find highly unlikely. Can't say more than that. I have an APFS disk, but it was formatted fresh.

Your links will stay fine.
 

KALLT

macrumors 603
Sep 23, 2008
5,118
3,168
APFS doesn’t support deduplication. Cloning is done only when copying files.

File-to-file hard links should be fine.
 

MrElvey

macrumors newbie
Feb 22, 2010
25
1
There's a major problem I worry about (and you may have already stumbled past or need to worry about): APFS support for preexisting deduplication! I have deduped a lot of things already by creating hard links over the years. And I read that APFS DOES NOT SUPPORT hard links to directories. If I recall correctly, a significant number of the hard links I created are to directories. (I haven't checked).
 

TETENAL

macrumors regular
Nov 29, 2014
207
210
As the title suggests I will convert all my HFS drives (internal and external) over to APFS.
Don't do it. Only convert the internal boot drive if it is a SSD. That is what Apple suggests.

APFS is not yet ready for spinning drives.
 
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h9826790

macrumors G5
Apr 3, 2014
14,125
6,744
Hong Kong
Don't do it. Only convert the internal boot drive if it is a SSD. That is what Apple suggests.

APFS is not yet ready for spinning drives.
IMO, APFS is not even ready for SSD (as OS). I tried that since HS official launch, and finally go back to HFS+ about a month ago because slow boot, Finder micro hang, or even HDD mount issue (the HDD is HFS+, but if the SSD boot drive is in APFS with TRIM enabled can cause my HDD disappear after warm restart).

And now, I went back to HFS+, and I am a happy HS user.
 

casperes1996

macrumors 601
Jan 26, 2014
4,901
2,766
Horsens, Denmark
There's a major problem I worry about (and you may have already stumbled past or need to worry about): APFS support for preexisting deduplication! I have deduped a lot of things already by creating hard links over the years. And I read that APFS DOES NOT SUPPORT hard links to directories. If I recall correctly, a significant number of the hard links I created are to directories. (I haven't checked).

This is from the man page for ln
By default, ln makes hard links. A hard link to a file is indistinguish-

able from the original directory entry; any changes to a file are effec-

tively independent of the name used to reference the file. Hard links

may not normally refer to directories and may not span file systems.

As you can see, HFS+ allowing hard links to directories is non-standard, and APFS acts more like what is expected in that case. Symbolic links should've been used, or a new directory created containing hard links to the items inside the other directory
 

choreo

macrumors 6502
Jan 10, 2008
412
156
Midland, TX
So, if I am reading some of the above comments correctly, I cannot install High Sierra on an HDD? It has to be an SSD?

I am asking because I have just installed High Sierra on an internal HDD in my Mac Pro and it is migrating files from Time Machine as I write this. Are you saying this process will fail?
 

casperes1996

macrumors 601
Jan 26, 2014
4,901
2,766
Horsens, Denmark
So, if I am reading some of the above comments correctly, I cannot install High Sierra on an HDD? It has to be an SSD?

I am asking because I have just installed High Sierra on an internal HDD in my Mac Pro and it is migrating files from Time Machine as I write this. Are you saying this process will fail?
What comments made you think that? HS can run just fine on an HDD. But not APFS
 

choreo

macrumors 6502
Jan 10, 2008
412
156
Midland, TX
What comments made you think that? HS can run just fine on an HDD. But not APFS
I get it even from articles like this one:

I have been running HS on my internal SSD (on PCI card) formatted with APFS for a couple months now (of course the system "sees" the SSD on PCI as external?). I have been using Carbon Copy Cloner to back up that SSD to a regular Firewire External Hard Drive that was formatted with HFS+ and I discovered last night that I could not boot from the external hard drive with HS installed on it?

HS Installer automatically converted my SSD to APFS during the initial install.
 
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