Optimizing Linux with cheap flash drives

Posted Feb 19, 2011 18:23 UTC (Sat) by aleXXX (subscriber, #2742)
In reply to: Optimizing Linux with cheap flash drives by arnd
Parent article: Optimizing Linux with cheap flash drives

You mention read/write speed around 15 MB/s.
How does that fit together with the number between 150 and 350 MB/s which are listed for SSD drives e.g. on alternate.de ?

Actually I can remember that when writing to raw NAND we had also rates somewhere in the 10 to 15 MB/s range.

Alex

Optimizing Linux with cheap flash drives

Posted Feb 19, 2011 20:03 UTC (Sat) by arnd (subscriber, #8866) [Link]

15 MB/s is typical for good SD cards (e.g. Class 6), which are limited by design to 20-25 MB/s anyway (UHS-1 SDHC will be faster, but is still rare today). High-end SSDs can be much faster for a number of reasons:

* SATA is a much faster interface than SD/MMC
* NCQ and write caching allows optimizing the accesses by reordering and batching NAND flash accesses
* Using SLC NAND instead of MLC improves raw accesses
* Using multiple NAND chips in parallel gives a better combined throughput
* Expensive microcontrollers on the drive can use smarter algorithms

All of these cost money, so you don't find them on the low end drives that I analyzed.