I wish to reformat my HDDs (2x 1 TB WD) from the OS Extended (Journaled) format to the new APFS, and to make a stripped RAID with these disks. One of these disks is currently my boot drive. The machine is the Mac Pro 5,1 Tower (not a flashed 4,1), running High Sierra. Blackmagic shows that I currently get about 40 MB/s read and write on these old SATA drives, and expect the conversion to give me at least a doubling of this dismal speed (not much, I know, but until I can afford a PCIe SSD this will have to do). I need to know the best fail-safe way to make this migration, bringing over both the data files and software from my Timemachine backup. Some of my software is not available for re-installation which would be required if, for some reason, this migration fails. Hence I am a little hesitant to reformat my boot drive until I know that this can be done successfully. Please advise (and reassure) me.
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Convert to APFS
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APFS on HDDs has slower performance over HFS+. This is largely because of how APFS handles metadata and its copy on write. I suggested keeping your HDDs on HFS+.
A stripped RAID in general will give you double the performance. But because you're still using HDDs as the storage devices, you'll get worse overall performance with APFS. You can make a stripped RAID with HFS+ and it'll be faster. Just note that with a stripped RAID you double your chance of losing data if a drive fails. Make sure you have backups because if one drive fails, you'll lose it all.
I know that it can be done although I have never done it myself. I have erased my drive and reformatted it but never tried to save any of my data via Time Machine, probably because I'm too lazy. Lol. I just backed it all up on a USB. Good Luck
RAID 0 only gives you 2x performance on the sequential speed, but not the small read / write (e.g. metadata). And it’s independent to file system. So, it will be slower than HFS+
Convert or format? Format I think is pretty straight, convert should be impossible at this moment.
The only thing you can do is back up the partition and then use command line diskutil to remove the container. Then restore.
CarbonCopy Cloner is my goto for this type of thing.
Sorry to bump, but I just wanted to clarify that mirrored raid (RAID-1) can also double your performance.
The reason that RAID-0 (striped) doubles speed is because blocks are split between all drives, so are loaded from them all simultaneously, but this only really gives you a boost for large sequential access (e.g- movie files), for random performance it's actually worse as you're often reading more data than you need to. It also has no redundancy, so if a single drive in the set fails, you lose all the data on the array.
However, RAID-1 (mirrored) can also double your speed for sequential access, because appleRAID supports load-balancing. Basically because the data on all drives in the set is identical, macOS is free to load data from any drive it likes, so it can alternate accesses between them to balance the load. For large sequential accesses this can give basically the same performance as RAID-0, but you also get better performance for random small file access as well. Plus you have the added benefit of redundancy, so if a drive fails you don't lose any data, and can easily restore it by swapping out the failed drive for a new one of the same or larger size.
If you have an even number of disks with at least four, you might consider a RAID-10, in which case you basically use a combination of mirroring and striping to give you a mixture of performance and redundancy; you do this by taking two drives and striping them, then do the same to the other two, and then mirror the two pairs. Due to load balancing between the pairs any slow-down from striping is largely eliminated, while keeping the speed benefit for sequential access, plus if any of the striped pairs fails, the other(s) still have a full copy of your data.
How this will interact with APFS is a bit mixed though, and I'm not sure I'd recommend any kind of RAID configuration for APFS using spinning hard drives, but it depends a lot on how you'll be using them.
APFS can have poor performance on spinning disks, because when you write changes to a file, they are written somewhere else on the disk, which means to load the modified file may require loading from multiple different physical locations (adding seek time); a mirrored set will help with this a bit, but it'll still be slower than HFS+ where files are mostly written to the same physical location as much as possible. None of this matters however if you're looking at storing data that doesn't change often, such as a media library where you'll only be adding or deleting files, rather than editing existing ones, in which case APFS performance should be just as good as HFS+.
Edit: To clarify, part of why I bumped is because this thread is a top result for searches on APFS performance on HDDs.
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