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SSD slow WriteFile() with "FAST IO DISALLOWED" (Win11)

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Observing some strange slowdowns when copying files...

1. AS SSD Benchmark write speed around 200mb/s
Process Monitor shows that benchmark writes to file and WriteFile () result is always SUCCESS. Procmon also shows, that file is created with "nocache" attribute.

2. Copying single 90gb file to external SSD using FAR Manager, write speed is 100mb/s. Haven't checked procmon yet. Was wrong about this one, speed is much lower. Disk goes to 100% load in task manager and speed drops.

3. Copying a lot of files using 7-zip (zero level compression) 12mb/s to external SSD, 20mb/s if writing to same disc. ProcMon shows that large 7z archive has a lot of WriteFile() calls, and some of then has FAST IO DISALLOWED result. 99% sure will work fast after clean install, but then something may be broken again. No defender, indexing, stopped all services with clickable stop button. Want to avoid reinstalling the system.

So what's strange is that making 100gb zero level compression file on the same disk as input files and then copying big file to external ssd is faster than outputting 7z archive directly on external ssd. Using this backup process since windows 8, and it's always something new with slowdowns. My 10-year old notebook does same backup with 7z at 90mb/s, and slowdowns was due to indexing or defender and resolved fast enough by disabling them.

Maybe something to do with sata ahci controller vid_8086 pid_4dd3. I couldn't find any driver, so currently it's Microsoft standard sata ahci driver.

Computer is noname n5095 laptop, 16gb ram, replaced SSD with a faster one.

What could it be? I tried to disable "MSI" through registry key, monitored disk writes and reads, disabled/enabled caching policy, but it's still unclear what makes copying process so slow.

I couldn't stand it, made a backup and reinstalled Windows. There is an improvement, backup speed is around 60mb/s, but not reaching 100mb/s.  It turns out that "fast io disallowed" for writes is not related to this problem. Most likely it is somehow related to SSD firmware, I'll try to search for updates. This doesn't explain why AS SSD benchmark always shows the same good results though.

Too little info.
How is the external SSD connected? eSATA? USB? (level?) to SATA or m.2 SSD?
Which model of SSD?

Just a note on SSDs: A lot of cheaper SSDs even come without DRAM cache these days and reach their advertised speed by using multilevel flash as single level. But only a small amount of the storage capacity is used this (fast) way. The regular quad level memory is quite slow.
So when copying a really large file, you immediatly saturate the DRAM cache, very soon saturate the single level area (a couple of GB, max) and then run into quad level writing, which is really slow. Depending on the model it might be way slower than a mechanical HDD.

Benchmarking usually runs only on DRAM or single cell has no meaning when doing large transfers.

And, another thing, the SSD controllers get very hot when running a maximal transfer - going into thermal throtteling is common. (This is rather an issue with fast M.2 and not so much on SATA SSDs...)

Which SSD? Is everything OK in SMART?
Cheap ones have slow NAND, no DRAM cache, can perform like a slow USB drive!

Internal ssd is Kingspec nt-512 (2280) ngff. I will check smart. Something tells me that if I use ReadFile() and WriteFile() the same way as AS SSD Benchmark, then copy speed will be around 100-200mb/s for big files. I think that something if broken in Windows when using this chipset.

External SSD:
1) Cuso c5s-evo 480gb in Jmicron usb 3 generic enclosure. This one gave around 100mb/s during backups when connected to an old Inspiron-3542 laptop.
2) Product page vanished, I'll check later. Jmicron usb 3 enclosure. This one was main SSD of Inspiron-3542. CD-ROM was replaced by another 128gb SSD. Copy speeds always was satisfactory.

Now, using a newer PC I observe slightly better AS SSD Benchmark results, but copy speeds became much worse. I always used 7-zip's "store compression" level for backups, because it generates single file on external drive and provides significant copy speed boost compared to normal copy/paste.


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