Currently, that consists of a total of 11 TB across 7 SSDs, of which around 5 TB contains files. To assess its success, I have surveyed all the storage accessed by my iMac Pro, looking for errors. This can’t of course guarantee that errors never occur in an APFS file system, but should eliminate this process of steady degradation and eliminate the need for such routine maintenance. On SSDs, copy-on-write actually helps the essential process of wear levelling, to ensure that the number of erases is spread evenly across storage blocks. The disadvantage of doing this is when APFS is used on hard disks, which suffer serious fragmentation in their file system metadata. Because it’s primarily designed for use with SSDs, for which seek times and fragmentation aren’t a concern, what APFS does is to write changed metadata to a new location on disk, and only when that has been completed successfully is the original metadata released for re-use, a process known as copy-on-write. One of the major changes introduced in APFS is in the way that its file system metadata are changed.
#Diskwarrior for os x full#
The need for this reduced substantially with journalling, but it was a workaround rather than a full solution, and directory maintenance remained popular. Prior to its introduction, it was common for most crashes to result in at least minor damage to file system metadata, and many of us routinely rebuilt its directories after each crash, or as periodic maintenance, to prevent those accumulating until serious errors resulted. Should anything go wrong while changing file system data, such as a crash or even worse a kernel panic, that’s likely to leave the file system metadata with a mixture of the old and new, resulting in an error.Īpple addressed this by introducing journalling, in which the file system makes each change first in a record in its journal, then to the catalogue in the file system metadata. This is efficient, but inherently prone to error.
As a result, in common with most file systems designed for hard disks, it defaults to overwriting data when changing it, notably in the file system metadata. While MFS was designed for use with 400 KB floppy disks and couldn’t cope with storage larger than 20 MB, HFS+ was intended for hard disks larger than any currently available.Īmong the problems with hard disk storage which HFS+ tried to address were seek times, fragmentation, and limited space. HFS+, which APFS has all but replaced, was the successor to HFS, which in turn replaced the Mac’s original MFS in 1985. This article considers where APFS is today in Big Sur, which has now reached version 1677.81.1. First rolled out in a bold and daring move on 27 March 2017 to unsuspecting iOS users, we’ve been running it on our Macs since upgrading to High Sierra in September 2017. Later this month Apple File System (APFS) will be four years old.
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