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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Notebooks > formatting a SSD unnecessary?

formatting a SSD unnecessary?
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iomatic
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Nov 5, 2008, 02:40 PM
 
In anticipation of receiving a new SSD-enabled machine, I was considering reformatting and reinstalling in the OS as I have done in the past (not always; sometimes). Now that I think about it, this seems unnecessary. Are there still bad sectors, and other defects in SSD to consider anymore?

Defragmentation, still (doubtful, right)?

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Big Mac
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Nov 5, 2008, 02:42 PM
 
The drive still needs to be HFS formatted.

"The natural progress of things is for liberty to yield and government to gain ground." TJ
     
iomatic  (op)
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Nov 5, 2008, 06:08 PM
 
Well, yeah, I expect it to ship that way from Apple... my question is: will a reformat be wastefully redundant?
     
CharlesS
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Nov 5, 2008, 07:18 PM
 
It will waste the drive's write cycles, thus shortening its life by some (probably very small) amount. If you use the "Zero All Data" option, then more so.

I'd probably just leave it alone as long as it's working.

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mduell
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Nov 5, 2008, 07:40 PM
 
I don't understand why you were reformatting for the reasons stated in the first place. Have you had any problems with getting heavily fragmented drives from Apple? Or had reformatting catch any bad sectors?
     
Tomchu
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Nov 5, 2008, 07:41 PM
 
File systems don't know or care what kind of media they're on; having to format a blank disk with a particular filesystem format is obviously still required. Fragmentation is as likely to happen on an SSD as it is on a platter-and-head disk, as fragmentation is a file system-level thing.

Where SSDs help is that a fragmented file won't have as big an impact on read performance as it would on a typical hard disk, because the seek time of an SSD is much, much lower than a hard disk.
     
iomatic  (op)
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Nov 5, 2008, 07:48 PM
 
Originally Posted by mduell View Post
I don't understand why you were reformatting for the reasons stated in the first place. Have you had any problems with getting heavily fragmented drives from Apple? Or had reformatting catch any bad sectors?
Rarely have I done it. My kids' old iBooks needed a full rewrite every time to avoid the Airport menu bug (you'd get a spinning beach ball after waking/etc. when first used after a few days-- we're talking refurbs and brand new)-- actually on my MBP at one point also. Could've been a system-level bug, but a full zero out and reinstall always fixed it-- and NEVER came back. Ever. Surely, this is not a hard drive issue, and probably unrelated. I just know that platter-based magnetic media is very prone to actual physical issues, more so than SSD, so I have to ask, is it worth a clean install procedure of a sort?

Seems not?
     
Spheric Harlot
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Nov 6, 2008, 04:20 AM
 
Originally Posted by Tomchu View Post
Where SSDs help is that a fragmented file won't have as big an impact on read performance as it would on a typical hard disk, because the seek time of an SSD is much, much lower than a hard disk.
From what I've read, fragmentation is pretty much irrelevant on an SSD at, since it doesn't matter where a sector is read from - there is no mechanical head that needs to be moved to that space.

At least in terms of performance, defragmentation should be once and for all a thing of the past. There may still be advantages for file recovery, but that should come from a backup, anyway.
     
The Godfather
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Nov 6, 2008, 08:48 AM
 
If you don't care much about security, skip the zero-all-data option if you format. It will decrease your overall write operations life by 0.01% in one single shot (10000 write operations per block*).
If you find a defragmentation utility, DON'T USE IT. Since it shuffles and re-shuffles every single file until all files and free space are defragged, many blocks may be written onto thousands of times, bringing that block closer to its death.
If you find an SSD with wear leveling feature, it will spread the harm to all blocks in the drive, delaying the appearance of bad blocks until all blocks are ready to die.

*subunit of a sector, generally a few kB large, and minimum write unit. NAND flash cannot be written on a byte by byte basis. The OS needs to read a block to RAM, erase the block, then write the changed contents over, even if you changed a single character in your small document.
     
Tomchu
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Nov 6, 2008, 06:12 PM
 
Originally Posted by Spheric Harlot View Post
From what I've read, fragmentation is pretty much irrelevant on an SSD at, since it doesn't matter where a sector is read from - there is no mechanical head that needs to be moved to that space.

At least in terms of performance, defragmentation should be once and for all a thing of the past. There may still be advantages for file recovery, but that should come from a backup, anyway.
There's still a lot less overhead to do when the file is continuous, as opposed to:

1. The file system driver has to look up the location of all of the fragments in the file system table
2. The OS has to issue multiple read operations to the device
3. The device is unable to use read-ahead or multi-block reads for the entire file

Originally Posted by The Godfather View Post
(10000 write operations per block*).
If it's an SLC SSD, it'll be closer to 100,000.

Originally Posted by The Godfather View Post
If you find a defragmentation utility, DON'T USE IT. Since it shuffles and re-shuffles every single file until all files and free space are defragged, many blocks may be written onto thousands of times, bringing that block closer to its death.
That's not how any intelligent defrag utility works. They'll reshuffle only the files that are fragmented, or to make room for a larger continuous file. No block will be written to "thousands of times". Anyone can tell that much just by looking at Diskeeper's status window. :-P
     
CharlesS
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Nov 6, 2008, 06:19 PM
 
Originally Posted by Tomchu View Post
There's still a lot less overhead to do when the file is continuous, as opposed to:

1. The file system driver has to look up the location of all of the fragments in the file system table
2. The OS has to issue multiple read operations to the device
3. The device is unable to use read-ahead or multi-block reads for the entire file
I'd expect the effect to be negligible compared to a regular hard drive. The major thing that slows things down there is the read and write heads moving around, which obviously doesn't apply to a SSD. I would be extremely surprised if fragmentation was at all noticeable on a SSD under any conditions.

If it's an SLC SSD, it'll be closer to 100,000.
If I'm correctly informed, SLC SSDs are not currently available in 128 GB sizes, and if they were, they'd be quite expensive. All of the drives Apple is bundling are almost certainly MLC.

That's not how any intelligent defrag utility works. They'll reshuffle only the files that are fragmented, or to make room for a larger continuous file. No block will be written to "thousands of times". Anyone can tell that much just by looking at Diskeeper's status window. :-P
I haven't used any defrag utility since Speed Disk back in the OS 9 days, but as I remember it the blocks near the end of the disk would get written to a lot, since if there's already data in the location where the defragger wants to put something, it has to be temporarily moved somewhere else until it can be placed elsewhere, and that place for temporary data tended to be near the bottom of the drive more often than not.

Regardless, any defrag operation is going to cause quite a lot of writes, which due to write leveling will get spread all over every block on the disk. It will reduce the life of your SSD by some degree, however small, each time you do it, and since the benefits will be slim to none, I do not recommend defragging a SSD.

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Tomchu
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Nov 6, 2008, 07:47 PM
 
All in all, I agree that a fragmented file system on an SSD probably has a negligible impact on performance. The real performance improvement (and hence performance hit if fragmented) for SSDs will come with true, multi-threaded, non-blocking file systems. An SSD can read/write multiple NAND channels at once -- our current filesystems were all designed around the concept of a single read/write head.
     
   
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