I'm guessing there's no hard limit, but I know that performance degrades when you put too many files into a single Windows folder. Does anybody have any good rules of thumb for when it becomes noticeably slow to open a file?
Assuming NTFS here, in which case the technical limit is around 4 billion files. And until you go over 10s of thousands per directory you really should not worry too much.
Note however that programs like Explorer suffer much sooner than 10s of thousands, because they try to access all files in a given directory to get meta-data, etc.
Opening a file won't be very slow regardless of how many files you have in a folder. What certainly is going to kill you is enumerating files in that folder. So taking a look at the contents of that folder with Explorer, Far, dir, Get-ChildItem, whatever.
That being said, I have around 2.5k files and folders in my temp folder and display is instantaneous, so that's apparently still a small number.
ETA: Ok, just tried it, 10000 files in a folder take around one second to open that folder in Far, this and 20000 files don't even matter in Explorer.
Look here. It says for files per volume, not per folder.
- NTFS: 2^32 - 1 = 4.294.967.295 files
- FAT: Approximately 4 million
For a decent consumer grade hardware, 150K files per folder is the number I have come across as per Windows 10 build 18362.356 using its native Explorer on a WD Blue 4TB hard disk drive in NTFS (partitioned 2 TB + 2TB ). For all files at fixed size of 24KB and filetype .7z . 150K is the number of files the explorer can display, I can select and do some operation. Any larger in the same folder and the windows explorer starts crawling.
It's highly likely this number is dependent on the File Explorer, filesystem, OS, drive speed, drive type (SSD/HDD/Raid HDD etc.) and also the supporting hardware itself like the Storage controllers, CPU and health of the SATA cables (or PATA or m.2 socket). For exammple the SouthBridge controllers would probably have a slower performance than CPU/NB controllers and connecting the drive to the SB should be a slower performance overall. Also 7zip's file explorer is much faster than Windows File Explorer in selecting huge number of files, in the range on 100Ks. I am not certain about the file sizes and if they will or won't affect the read time but my other folders with 1000s of images per folder take a long time, is it due to them having filetype of .jpg/.png etc. or is it due to their huge sizes or is it due to the explorer trying to generate thumbnails for them I am not sure. I have seen windows skips generating thumbnails for images >20 MB so that can be a valid concern.
If you want to be on the performant side, having about 50K files per folder in my opinion would be better as you wouldn't need to worry about different explorer's or os' etc. causing the file explorer to crash or take minutes of selection/display time.