Hacker News Reader

Comment by uuid | Hacker News Reader

SSDs do degrade by around factor ten (!) in write performance when full, although not in read performance. (Tested this with an x25-m).

Sadly, recovering from a fragmented SSD on OSX right now involves opening the machine and booting linux. (I tried that, and it works: http://forums.macrumors.com/showthread.php?t=841182)

View on HN

I'm not saying they don't degrade... just when they do, the performance is still so off-the-charts when compared to a hard drive that it's crazy to obsess over it.

And 10X sounds high to me - what sort of benchmark are you running? Most of the benchmarks I've seen put the hit at around 20 - 30% in random writes...

Back when I tried that I simply used xbench - the 4k block writes went below 10MB/s. I don't have the exact numbers, but I do remember that mac os took > 30 seconds of spinning wheel to boot, compared to 1-2 usually. BTW, filling the disk is as easy as performing "erase free space" with Disk Utility.

That doesn't seem typical - I'm using an 160GB X25-M G2 and have almost certainly filled the drive at this point (been running with less than 15% drive space free for a while, I leave hibernation on, installed and removed Boot Camp, etc.) and I'm still getting ~55 - 60MB/sec 4k sequential writes and ~60MB/sec 4KB random writes with the latest firmware in Xbench. I'd think booting would be mostly reads with a few writes here and there, too...

Although the 160GB has a slight write advantage over my 80GB G2, it appears those last 15% make quite a difference. That wouldn't be totally out of line from how regular HDs behave once they approach 100% utilized capacity. SSDs (the intel ones at least) have a buffer of cells that are inaccessible to the OS (that buffer is larger on e models), maybe that's double for the 160?

My X25-m died after 3 months of use, and I had the hd nearly full.. And I thought I would have never have to make backups again ;)

Reply on news.ycombinator.com