Fragmentation on initial copy/defrag questions

[Hastor]

I've just set up my first array and am currently still migrating the initial data into it. However, I currently have about 25 TB of data, spread over 3 data drives, with default allocation settings (high water, default folder split). I've been doing nothing but copying sets of files to an empty array. One file at a time from another network PC on a single connection, not writing multiple files at once. Why then, when I check the fragmentation of each individual disk, it is at 5-8% already? I must admit I haven't worked with large xfs volumes or even ones on mechanical disks, so I'm not used to what to expect. However, in systems like FAT32 and NTFS, copying files onto an empty drive usually results in little if any fragmentation. Copying the data off a drive and back on is typically one method of defragmenting as well, so why are the first files written to an array fragmented so much already? I am referring to file fragmentation, not folder fragmentation as well.

 

I also have seen just snippets of info regarding defragmenting array drives. I'm not clear on whether it is safe to do without needing to rebuild parity. I saw one post that said it was, but they didn't mention whether they were using dual parity, which I am, and I understand there are cases where parity might need rebuilt with dual where it wouldn't with single. I'd rather not leave things in an unprotected state in order to defrag, as that protection is the main purpose of the array, but would like to keep my disks from becoming too fragmented over time. While I'll be using it mostly as a backup, there will be times where I need to delete a bunch of small files to make room for a large one etc. If I defrag an array disk, does that still get detected and update the parity drives along the way?

Edited May 8, 2021 by Hastor

[John_M]

There are a few threads on the forum about XFS defragmentation. Here's one you might like to read: