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Comment by sumeeta | Hacker News Reader

Is there really a serious issue in the way OS X handles SSDs?

I think I want to replace my MacBook’s hard disk with an SSD, but I’m afraid of having to spend hours rigging out the best configuration. Do you have to play with settings if you order a Mac from Apple with an SSD pre-installed?

It seems like if I want to just plug an SSD in and get on with my life, I’ll have to wait for an OS X update. Unless this is all just PC-ricer talk that’s safe to ignore…

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I installed an SSD in my MBP some months ago, and it is fantastic. Just do it. Don't worry about hacking the settings--the OS folks at Apple will eke out the last few percent of perf for us when they get around to it.

As long as you leave plenty of free space, SSDs work great out of the box. Don't ever fill them (something beyond 80% capacity), or you will crush performance. The tweaks in the article are attempts to optimize for the last 2%, but in no way necessary.

Since you're going to be reading and writing to the drive repeatedly, the drive is always going to hit the write performance crunch no matter what you do (unless you support TRIM - Windows 7 does with the correct drivers, OS X does not, not sure about Linux).

However, even degraded, write performance of a modern SSD will still make a hard drive look like yesterday's news - so honestly, I wouldn't even worry about it at all.

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)

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 ;)

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?

Most of the tweaks in the blog article have little to do with SSD. I seriously doubt any of the tweaks in the article will have any longer term effects on the actual usage of the SSD.

They are all pretty much designed to minimize the amount of writes to the SSD. This is more about extending the longevity of the SSD than anything else.

I'm guessing most users will upgrade their hard drives & laptops before you run out of write cycles on it. Silicon typically drops in price per gig faster than magnetic platter discs do...

You can indeed get a SSD in a Mac Air as an option. Does Apple treat those different in OSX? I'm not sure.

I replaced the mechanical harddisk in my MacMini with a SSD about a year ago. It broke down last week. I don't think OSX is to blame, since I put the same model SSD in my Windows and FreeBSD machines at the same time (the FreeBSD box is always on and pretty busy), and no problems there yet. Except for the 'noatime' I didn't take any special precautions.

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