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Apple Desktops Discussion of Apple's desktop machines including Mac Pro, iMac, Power Mac, and mini

Very slow SSD speed in 2010 imac


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jwindard1990

 
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Hi, wonder if anyone can help or tell me why my SSD is so slow in my imac
Its a 2010 27" iMac so i know its only sata II not sata III
The SSD is a corsair force 3, i didnt expect to get the very high speeds obviously but the write speed is actually half of what my standard 1tb HDD is, which comes out around 120mbs and the SSD comes out at around 60mbs, this makes so sense to me...
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File Type: png DiskSpeedTest.png (360.6 KB, 28 views)

iMac 27" 2.8Ghz i5 Quad, 12gb, ATI 5750 1Gb
iPad 32Gb, iPod touch 4G 32Gb
iPhone 4s 32GB, Apple TV 2G
Many other Apple bits...
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scottmcp432

 
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First make sure you have the latest firmware installed for the SSD. Many SSD's, such as yours, which use the Sandforce controller have had problems in the past which required updates from the manufacturer. If you purchased this drive recently it was probably shipped with the latest firmware but you should verify this yourself. Here is a link to a thread started by someone having the same issue as you.
https://discussions.apple.com/thread...art=0&tstart=0
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BSD Meister

 
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It sounds like it's lacking TRIM/wear leveling support. The problem with SSDs is that they're a moving target - the technology is still changing.

On a standard hard drive, when a block of data is marked as erased, it isn't really erased unless it's over written. When a block of data has been marked as erased, it's block identifier is put into a queue, and the next time a write operation is performed the OS will search out the most sequential list of available blocks and use them. If the IDs that had previously been marked as "erased" it means they're available and the OS can over write them. This is why if you want to make sure no one can recover your data you need to zero the drive, because that will overwrite every single sector on a hard drive with binary zeroes.

This is not the case with SSDs. When a block of data is marked as erased, the drive has to first identify the block, then erase it, and THEN it's available for use...it isn't just readily available like it is in a regular hard drive. Typically what seems to happen on the older SSDs is that they actually don't start actually erasing and zeroing any of the blocks of data until they've all been used once. At that point, every time a write operation takes place, it first has to physically erase the block(s) and then write to them. This is time consuming and slows the drive down.

If the drive has real TRIM and/or wear leveling support, what will happen is that as blocks of data become marked as erased, rather than waiting for the drive to cycle through all available blocks, it runs a low priority background process that will "clean" the previously erased blocks with minimal interference to the user. Wear leveling keeps track of the usage of each block to ensure they're all getting used evenly (hence the "leveling" in wear leveling).

As I said, SSDs are still a moving target. TRIM and wear leveling is only supported on Mac OS X in some drives and some OS versions. If they aren't adequately supported, I believe the process is to clone the SSD to a regular hard drive, completely re-initialize the SSD, and then clone it back from the hard drive to the SSD.

I'm going to steer clear of SSDs until all the kinks seem to be worked out. This is one of them, but another one is where an SSD just "gives up the ghost" and seems to do a complete re-initialization on itself for reasons known only to the SSD.

Keep good backups!
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harryb2448

 
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OP Did you by any chance clone the contents to the SSD? OWC technicians are very firm in their directions clean install be carried out only.

Hang on to those original install discs like grim death! Using OS X.7 or later make a bootable USB thumb drive before running Installer!
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BSD Meister

 
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Like I said, SSDs are a moving target. OWC probably, or at least seems to have the best support for Mac SSDs, but what they say and state only applies to their own drives. There's no reason for me to doubt what scottmcp432 says, but what he says needs to be verified with the particular unit you're using.

You can do a Google search for something like "Mac SSD" and you'll get a myriad of answers. The problems I see with this technology are as follows:

1. It really isn't cross platform supported yet - Most of it (as usual) is targeted for Windoze.

2. In some cases, they assume you can install a new controller in your system that supports their hardware (once again, more of a Windoze thing, unless you have a Mac Pro, and even there the support options are limited)

3. There isn't a lot of documentation available for Apple users regarding 3rd party SSD installations. As usual, Apple likely wants you to have them install one of their approved drives by their people at their facilities and pay their prices ($$$$$$)

There is a freeware, or perhaps I should call it "donationware" application available on the web that inserts kernel extensions to support TRIM, Here's a link for one of them (I have no experience):

Trim Enabler

Another interesting article is this one:

Maintaining SSD drives in OS X | MacFixIt - CNET Reviews

Installing kernel extensions for I/O bound devices, especially with reports of kernel panics (if you look into some of those links above) gives me a very uneasy feeling.

I'll conclude with this remark: SSDs are a moving target.

Good luck, and I hope this is of some value to you.
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chscag

 
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Quote:
I'll conclude with this remark: SSDs are a moving target.
Well put and I fully agree. Which is one reason why I haven't jumped on the SSD bandwagon yet. Of course price is also a strong factor considering how expensive SSDs are. I'll stick with spindle drives for the time being.
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