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Newbie
Posts: 1
Registered: ‎09-17-2016

Re: USB Ultra Flair SDCZ73 32GB/ 64GB 3.0 - Write Speeed only 25MB/s

I don't understand why this thread is marked as "solved", when it isn't.

 

I found out the real reason with these write speed drops. This USB flash drive obviously uses some kind of cache, similarly as TLC SSDs use SLC cache. If you copy files that are smaller than cache size, you won't notice any speed drop. But if you copy files that are larger than cache size, cache will fill up, and flash drive will continue writing to drive's main slow NAND. You can verify that this is the case by cancelling of copying, and then immediatelly copying again - write speed will almost instantly fall down because drive hasn't had the time to clear the cache yet, so the drives continues to write to main NAND instead of cache. If you cancel again, give the drive half a minute or a minute, and copy again, it will start at the full speed because now again it can write to cache, because it had enough time to clear it.

 

So, when you copy files to drive, it will first try to fill the cache. When the drive is idle, content from cache will be moved onto slow NAND.

 

I have 16 GB Ultra Flair drive - it seems that it has 384MB of cache (I suppose 3x128MB).

SanDisk Guru
Posts: 2,408
Registered: ‎07-23-2010

Re: USB Ultra Flair SDCZ73 32GB/ 64GB 3.0 - Write Speeed only 25MB/s

[ Edited ]

An interesting observation marekic.

 

As for the thread being marked solved you will have to ask the OP.  He's the one who marked it.

Ed
Important files = Backed up files
Newbie
Posts: 1
Registered: ‎10-24-2017

Re: USB Ultra Flair SDCZ73 32GB/ 64GB 3.0 - Write Speeed only 25MB/s

I bought a 32GB Ultra Fit one. Its cache is 1GB.
I think its the best and only correct answer I've found after some days!
I test your solution and you're correct.
But it's not efficient way to reach highest performance of flash! Why?
Let's calculate!

You must let flash to SLEEP at least 30secs to clear its cache. If you don't stop copying, about 600MB will copy within this time.
Until now, normal method is 600, and pause/resume method is 0. Come on! I went ahead Smiley Very Happy

After this, the flash will resume with about 60MB/s. But after about 15-20 seconds, its cache will fill up again! Smiley Sad
In this time, the normal way copies about 400MB!

0+1000 = 600+400 Smiley Very Happy

So we should be a satisfied good boy and don't protest for speed drop of ultras -_-

Highlighted
Newbie
Posts: 2
Registered: ‎11-04-2017

Re: USB Ultra Flair SDCZ73 32GB/ 64GB 3.0 - Write Speeed only 25MB/s

[ Edited ]

The  "Up To" speed of 150MB/s are not specified to be Read or Write, refer to images

 

As the packaging states "Transfer a full-length movie in less than Blah blah Blah seconds", calculations may be assummed the specified speed is for both Read and Write ? 

 

This may be construed to be misleading product information.

In the Far East where people are a sticker for details and nothing but exactness is acceptable or they'll complain complain and complain some more, the Sandisk packaging DOES state both Read and Write information !

So the question to be asked with regard to Western packaging is "Why" ?

 

Ultra Flair 1.jpgSandisk Ultra.jpgSanDisk-Ultra-Flair-CZ73 Read_Write Speed.jpg