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AltecXP · Jul 11, 2010, 04:41 PM

I just ordered an OWC 256GB SSD to replace the HDD in my 15in i5 MBP.

Is there anything I should know or do to my MacBook before or after I install OSX on it?

Thanks, can't wait till I get it.

CharlesS · Jul 11, 2010, 04:59 PM

OWC has 256GB SSDs now? I thought they only had 240 and 480.

Anyway, installing OS X on an SSD is exactly the same as installing on a regular hard drive. The only preparatory step I'd recommend would be, if you're using Migration Assistant or something else to transfer your files to the new SSD, to clean up your hard drive, deleting old crap you're not going to use which is taking up space. Since OS X lacks TRIM support, performance is going to suffer if you write to too many of the blocks on the drive, so it's a good idea not to fill it too full. Hopefully Snow Leopard will get TRIM support in an update soon, which would negate this issue.

The one thing not to do would be to use the Zero All Data in Disk Utility or to ever run a defrag utility. This will write to every block on your drive and completely kill performance.

The only thing to do after installing OS X on the SSD will be to set a whole ton of login items and gawk at how your logins are still instantaneous. I have about 16 login items, and a ton of icons on the Desktop, and it still manages to pop right up. It's quite astonishing, actually.

AltecXP · Jul 11, 2010, 05:20 PM

Sorry it is a 240GB, I'm just not used to these weird sizes yet.

besson3c · Jul 11, 2010, 06:14 PM

Did you buy the drive from Apple or from another vendor? I'm curious how the Apple store prices compare to NewEgg's...

CharlesS · Jul 11, 2010, 08:30 PM

Originally Posted by AltecXP

Sorry it is a 240GB, I'm just not used to these weird sizes yet.

Well, to be fair, it probably actually is a 256 GB drive. Some of these drives have a bunch of blocks reserved as spares so that it can continue to have some spare blocks to write to even after the drive has filled up, for performance and longevity reasons, leaving you with a smaller usable capacity than the true capacity of the drive.

Originally Posted by besson3c

Did you buy the drive from Apple or from another vendor? I'm curious how the Apple store prices compare to NewEgg's...

Since it's an OWC SSD, he presumably bought it from OWC. OWC charges $694.95. The OWC drives use the Sandforce controller, and the 240 GB Sandforce drives on Newegg range from $599 to $659.99.

P · Jul 12, 2010, 03:09 AM

Originally Posted by CharlesS

Well, to be fair, it probably actually is a 256 GB drive. Some of these drives have a bunch of blocks reserved as spares so that it can continue to have some spare blocks to write to even after the drive has filled up, for performance and longevity reasons, leaving you with a smaller usable capacity than the true capacity of the drive.

Actually, they all do that to some extent. SSD is flash storage, and flash storage is produced in power-of-two capacities. Storage is reported in power-of-ten mini-gigs, and the difference - 7% or so - is just enough to be used as spares. Of course, the number of Flash chips doesn't have to be power-of-two - Intel designs their drives around 5, 10 or 20 flash chips.

all2ofme · Jul 12, 2010, 06:15 AM

Originally Posted by CharlesS

The one thing not to do would be to use the Zero All Data in Disk Utility or to ever run a defrag utility. This will write to every block on your drive and completely kill performance.

Is there a reason that zeroing all data would have a negative effect if you're installing the OS from scratch on your drive? If it doesn't improve things that's one thing, but if it actively degrades performance that's another.

P · Jul 12, 2010, 06:55 AM

Originally Posted by all2ofme

Is there a reason that zeroing all data would have a negative effect if you're installing the OS from scratch on your drive? If it doesn't improve things that's one thing, but if it actively degrades performance that's another.

It actively degrades performance. A lot.

This is of course specific to SSDs - HDs have no problem.

AltecXP · Jul 12, 2010, 11:35 AM

I have an SSD I use on my Windows box, it used to get 7.3 in the Windows Experience Index (WEI), and the i moved it to my macbook to try it out. I Zero'd it out then installed OSX, I then put it back in my Windows desktop and installed Windows back on it, it now gets seen at 7.5 in WEI, so it definitely didn't turn anything short term.

P · Jul 12, 2010, 12:06 PM

The difference is that Windows supports TRIM. When reformatting a drive - which you have to do if you will install Windows on it - the entire drive gets sent the TRIM command which basically resets the drive to initial state. Mac OS X doesn't support TRIM yet, so zeroing it (not just reformatting) will kill performance.

CharlesS · Jul 12, 2010, 02:08 PM

Originally Posted by all2ofme

Is there a reason that zeroing all data would have a negative effect if you're installing the OS from scratch on your drive? If it doesn't improve things that's one thing, but if it actively degrades performance that's another.

A major difference in SSDs vs. HDDs is that while HDDs have no performance penalty from overwriting a block that already has data on it, on an SSD that involves first erasing the block, then writing new data on it. Writing to a virgin block that has no data on it, by comparison, only involves writing the data with no erasing, and consequently is a lot faster. In order to maximize performance (and also to prolong the life of the drive), SSDs use something called wear leveling, in which the SSD only writes to virgin blocks for all write operations, and doesn't start reusing old blocks until every block on the drive, including the spares, has been written to once. At this point write performance will degrade due to the need for constant erasing (although read performance will still be extremely fast).

In order to solve this problem, modern SSDs support a command called TRIM. This command allows the file system drivers to inform the SSD when a file is deleted, telling it what blocks the defunct file occupied. The SSD can then erase those blocks at its leisure, restoring them to the unwritten state, and when it comes time to write to those blocks again, it'll still be just as fast as when the drive was new. Unfortunately, the OS and file system drivers both need to support TRIM, and while Windows 7 and Linux both support it, OS X does not. However, artifacts have been showing up in Snow Leopard that seem to hint at future TRIM support, such as the yet-unimplemented doDiscard() function in IOBlockStorageDevice.h and the "TRIM Support:" field in System Profiler that currently always says "No". When I bought an SSD, I was gambling that the TRIM support will be implemented in a 10.6.x update before I end up writing to all the blocks on the drive. I think it's probably a decent bet, but I'd try to be economical about really large writes to the drive in the meantime. In the worst-case scenario, of course, it's possible to back up the SSD, boot into another operating system to secure erase the SSD and erase all its blocks, and then restore from backup, thus restoring the SSD's original performance. Using the "Zero all data" option in Disk Utility, however, will not do this — it'll just write zeros to every block on the drive, with the result that all the blocks now have data on them and the only virgin blocks are your spares (assuming all the blocks on the SSD were unwritten prior to the "Zero all data" operation), some of which you'll use up installing the OS. Needless to say, your performance will degrade very quickly after doing this, and as such this is the opposite of what you want. Defrag is also pointless since the files are going to be extremely fragmented anyway due to the wear leveling table, and will just cause tons of write operations, thus chewing up the free blocks on your SSD.

AltecXP · Jul 12, 2010, 02:56 PM

Does that mean if I partition it then the WIndows 7 part will be using Trim, but the OSX part wont?

P · Jul 13, 2010, 08:43 AM

CharlesS explained it rather nciely, I think. Heck, I'll quote relevant bit for you:

In order to solve this problem, modern SSDs support a command called TRIM. This command allows the file system drivers to inform the SSD when a file is deleted, telling it what blocks the defunct file occupied.

When a file is deleted under Windows 7, the operating system will send a command to the drive, informing it that that (filesystem) block is free and can be wiped as required. When a file is deleted under Mac OS X, no such command will be sent, and the block will not be wiped, degrading performance of the drive a little bit.

The issue is further complicated by one item that CharlesS didn't mentioned. SSDs are arranged into pages, which are 4K large (the same as a filesystem allocation block). These pages are then grouped into drive blocks of a larger size - usually 512K.

The SSD can write to an individual 4K page, but when deleting, it must delete an entire 512K drive block.

This means that if a 4K page needs to be deleted, the drive must copy the rest of the 512K block somewhere else first and then delete the entire 512K block. Without TRIM, that 512K block might very well be mostly things that should be deleted anyway. Because of this, the drive has to work much harder to move around pages that it might very well have skipped.

AltecXP · Jul 13, 2010, 10:26 AM

I decided to go with a 2nd SSD of 60GB just for Windows 7 in the optical bay (wish I could just fit in 2 1.8in drives). But the way I understand the answer to my last question is that ONLY the files that were deleted under Windows 7 will send back the TRIM command?

P · Jul 13, 2010, 11:50 AM

Yes.

CharlesS · Jul 13, 2010, 02:36 PM

Yes, but since TRIM support for OS X is very likely imminent, this should be only a temporary problem.

all2ofme · Jul 14, 2010, 05:15 AM

Great explanation guys - thanks. I'll sit tight with my slow (doh!) SSD until I get TRIM support, I think, rather than go through the hassle of backing up, blatting it somewhere that supports TRIM and then restoring.

It's fast as it is, but it's nice knowing I've got better performance to look forward to!

Love Calm Quiet · Jul 14, 2010, 11:41 PM

Originally Posted by CharlesS

Yes, but since TRIM support for OS X is very likely imminent, this should be only a temporary problem.

But how *temporary* will be the reserved-as-deleted blocks that I create now (while OS X does *not* provide TRIM): When OS X starts TRIMming, will there likely be a way to recover the (slow) previous erasures?

besson3c · Jul 14, 2010, 11:45 PM

What makes some of you certain that TRIM support in OS X is imminent? This thread has been very informative to me, I thank you for the education, but given that HFS+ is so extremely old and long in the tooth now it may not be trivial to make changes to it, no?

BLAZE_MkIV · 12:18 AM

Before this you don't ever bother to delete stuff of the media you delete it from the table of contents. TRIM tells the drive that it did "delete" the block so it can re-use it in wear leveling / caching etc or most importantly don't bother to read first when writing to preserve data that isn't there anymore.

When the computer deleted something from that location the second time the TRIM would kick in. You could also run the manufactures TRIM, utility of they had one, once once OS X supports TRIM.

TRIM doesn't have anything to do with the file structure on the disk, its a block level operation you'd add to the file system software.

CharlesS · Jul 15, 2010, 01:04 AM

Originally Posted by Love Calm Quiet

But how *temporary* will be the reserved-as-deleted blocks that I create now (while OS X does *not* provide TRIM): When OS X starts TRIMming, will there likely be a way to recover the (slow) previous erasures?

If/when TRIM support gets added, I would hope that Disk Utility would be updated as well to be SSD-aware, so that things like "Erase Free Space" would do the right thing. Failing that, you could just backup, erase, and restore, or you could just wait it out since, as BLAZE_MkIV pointed out, the problem would eventually solve itself as the blocks became overwritten and subsequently erased.

Heck, even if Disk Utility didn't get updated, all you'd have to do would be to create a huge file that took up the entire free space of your drive, and then delete it.

Originally Posted by besson3c

What makes some of you certain that TRIM support in OS X is imminent? This thread has been very informative to me, I thank you for the education, but given that HFS+ is so extremely old and long in the tooth now it may not be trivial to make changes to it, no?

As I mentioned, a "TRIM Support:" status line got added to System Profiler in 10.6.4. Before that, a "doDiscard" function showed up in IOBlockStorageDevice.h. The foundations appear to be (slowly) being laid for TRIM support in the OS.

At any rate, it doesn't have anything to do with the file system beyond the drivers needing to inform the disk when something gets deleted. This shouldn't be particularly difficult — I suspect the reason it's been taking this long is because of the necessity of thoroughly testing it before releasing it on the public. Obviously you don't want it trimming the wrong block and causing data loss. At any rate, I'd expect TRIM support to show up soon. Apple can't viably leave it out for that much longer, since they've been bundling SSDs with their machines for some time now.

P · Jul 15, 2010, 08:09 AM

Originally Posted by besson3c

What makes some of you certain that TRIM support in OS X is imminent? This thread has been very informative to me, I thank you for the education, but given that HFS+ is so extremely old and long in the tooth now it may not be trivial to make changes to it, no?

Well, it's about 5 years younger than NTFS, which got TRIM support...

For one thing it's not hard to do, and for another Apple has added far bigger features to HFS+ since it launched. There are weaknesses in HFS+, but it isn't unmaintainable in the sense that some of the old Classic code was.

AltecXP · Jul 15, 2010, 02:13 PM

SSD came yesterday and I started out with a clean install and migrated anything I need and anything else was copied to a backup drive. Currently using 90GB of 240.

I've only disabled the SMS, but I have to say everything feels SO much smoother and quicker, and also removing a 37* heat point in the laptop/under my palm is never bad.

If I could only find a way to drop 10* @load on the macbook I'd have a silent(aside from fan) and much cooler temp MacBook.

CharlesS · Jul 15, 2010, 05:06 PM

Originally Posted by AltecXP

I've only disabled the SMS, but I have to say everything feels SO much smoother and quicker, and also removing a 37* heat point in the laptop/under my palm is never bad.

It's sweet, isn't it? Be sure to fill up your Dashboard with widgets, then reboot, open the Dashboard, and watch them all instantly load.

Oh, and enjoy the instantaneous Spotlight searches too. I may finally get rid of Quicksilver, as it's starting to become redundant.