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SSD 'slowdown' once full?

M

mrrippey

macrumors regular
Original poster
Apr 7, 2009
242
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there are quite a few threads on SSD's and wanted to better understand the actual slowdown when SSD drives are full or near full.

When we hear that the SSD's slow down, it is to the point that it is much slower than the 5400RPM drives in the laptops now or is it a slowdown like 50% of what the SSD was when new, with space?

I ask this question because there seems to be three main issues with SSD's; price/GB, total size and this slowdown when full (lets not get into TRIM and all that jazz just yet).

Just wanted to get some insight from some of you who have say Gen 1 X25 or have OCZ Agility, Summit or some of the other drives (even the Samsung Apple provides). I mean if the slowest SSD is still 50% faster than a 5400RPM HDD, some people will actually go for that at a low pricepoint.

Thoughts?
 
thanks for the link. I did read that article before (very informative) but I wanted some real world benchmarks.

For instance, the Samsung that ships with MacBook Pro's do not have trim and slow down as they get full. If it started at 100 and after 70% capacity its speed is 40% of original, is 40% of an SSD faster than an average HDD.

That is what I would like to find out.

if 40% of an SSD is slower than an average HDD then makes getting a non trim SSD harder. If an SSD is always going to be faster than a HDD, then even with no trim or gc, the SSD experience is going to be better.
 
Slowdowns on SSDs don't occur mostly when they fill up. They occur mostly when you start deleting files and you don't have the TRIM command. SSDs nowadays can't delete individual files, they can only erase in pages of 512K bytes (even if you have a 4K file to erase)...

It's like a form of fragmentation comparable to what you see in normal magnetic rotating hard drives.
 
fehhkk, thanks for the clarification

so lets say the overall slowdown from all of these deletes diminishes speed of the SSD by 50%. Is that still much better than your average HDD?

Of course (with proper backups) you can wipe the SSD and restore it back to get a pristine running SSD again if the SSD slows down so much that is is nonfunctional.
 
mrrippey said:
fehhkk, thanks for the clarification

so lets say the overall slowdown from all of these deletes diminishes speed of the SSD by 50%. Is that still much better than your average HDD?

Of course (with proper backups) you can wipe the SSD and restore it back to get a pristine running SSD again if the SSD slows down so much that is is nonfunctional.
Click to expand...

Someone in another forum suggested this: Until OS X supports TRIM, install Win7, boot into it and let it "condition" the drive via TRIM overnight and continue using OS X without any performance hit. It will take some space on the HD -unless you weren't going to install Windows 7 on this- since you have the 80GB G2C1, but it will keep the drive in top shape until a firmware update from Intel and OS X support from Apple are provided in the future. Just a thought... It might be easier than just wiping the drive, restoring from backups, etc.
 
So let me get this straight:

if my primary boot drive is OSX but I have another drive which I can use as a boot disk and boot camp into Windows7 then it can TRIM my drive? That is assuming Windows 7 can read my Mac Drive.

Is that what ur thinking?
 
tenderidol said:
Someone in another forum suggested this: Until OS X supports TRIM, install Win7, boot into it and let it "condition" the drive via TRIM overnight and continue using OS X without any performance hit. It will take some space on the HD -unless you weren't going to install Windows 7 on this- since you have the 80GB G2C1, but it will keep the drive in top shape until a firmware update from Intel and OS X support from Apple are provided in the future. Just a thought... It might be easier than just wiping the drive, restoring from backups, etc.
Click to expand...

How does that work if they are on different partitions?

@OP SSD are still faster than HDD even once all the blocks have been filled. My suggestion is don't worry too much about it and just use it. In real world use I really doubt you will even notice a difference and only diminishes write speeds.
 
Not all SSDs are created equal.

One thing you can do that will help most SSDs is to leave extra space. If you buy a 120GB but are only using 60GB, use Disk Utility to shrink your partition down to 80GB or so, and only grow it when you start running out of space.

The extra space allows the garbage collection "room" to work. Think of it like a defragger, it needs space to reorganize data. The less space, the more likely that a lot of writes will chew up free blocks before the garbage collection can prepare them.

The cheaper the SSD, generally the worse the garbage collection, the lower the over-provisioning, the less sophisticated the internals are.
 
So I did experience some slowdown on my G2 after removing a bunch of files from my SL upgrade (basically removing about 1GB of language packs, and moving 60GB of data from the SSD, to my optibay HD)...

Initially, upon a fresh upgrade, I noticed 6-7 second shutdowns with apps open. After doing all those file deletions, shutdowns went up to 10 seconds more or less. Same thing with the boot up process.

XBench reported initially, a 270-275 score in the hard disk. After having a "fragmented" drive, I was scoring at most 200!

I did a clean install of SL last night, and things were much faster, back to the 270's range. A 70 point swing in XBench is considerable I think.

Not complaining, but it's very interesting to understand how SSDs slow-down compared to hard drives. Your SSD will definitely slow down when you fill up the drive, and then start deleting stuff (just like what I experienced).

I imagine once we have full TRIM support, we wouldn't experience this...
 
ayeying said:
SSDs do degrade over time and it will be slower by tons. Another thing to consider about.
Click to expand...

But what exactly is slower by tons mean? Slower then a 5400rpm drive? Would the speed reset by issuing a TRIM command/operation say in windows 7?
 
Unless I'm mistaken, the slowdowns should only affect writes and not necessarily reads.

And partitioning your drive seems silly as some cells are programmed as inactive so that they can be used for things like wear leveling and garbage collection. Partitioning your drive is like telling Intel, et. al. that you know better.
 
jdechko said:
Unless I'm mistaken, the slowdowns should only affect writes and not necessarily reads.

And partitioning your drive seems silly as some cells are programmed as inactive so that they can be used for things like wear leveling and garbage collection. Partitioning your drive is like telling Intel, et. al. that you know better.
Click to expand...

Correct. Write operations are affected, which is what I saw.
 
jdechko said:
And partitioning your drive seems silly as some cells are programmed as inactive so that they can be used for things like wear leveling and garbage collection. Partitioning your drive is like telling Intel, et. al. that you know better.
Click to expand...

Even the most advanced SSD controller today needs around 10% of the drive free to swap files in and out when when writing, to be efficient. Most drives on the market only manage around 7% at most and could benefit greatly from an increase to 10, 20 or even 30% before write amplification falls back to 1.

Newer Intel drives don't even come with a predetermined "scratch" area out of the box, they use all of the space that is still empty on the drive. Only when every page has been written to once does it then set aside the inactive cells that you mention.
 
Just so you guys are aware of the basics of garbage collection.

OS fill drives randomly this means for an SSD it has to erase a partially filled block before it can rewrite to that block...this adds an erase cycle and slows the drive.
So you bring in garbage collection, this allows the controller to look at the partially filled blocks from the LBA table and move the data from the partially filled blocks to other blocks writing the data sequentially so it fills blocks completely, it then issues a discard command to the blocks where data has been moved from so you can write to them at full speed.

The big deal with MLC is write cycles, each cell has around 10000 then you can read only from it.

So GC with its added write cycles will actually wear a drive out faster than one without BUT the drive will stay at full speed.

its a trade off

TRIM is far superior and when integrated into OSX will negate the need for GC...why?

as data is discarded those blocks will be marked as deleted and allow the OS to write at full speed, there will be still some fragmentation (hence never fill an SSD to full ;)) BUT you lose that added write cycle and as such the drive will live longer.

Its all a question of what is more important to you...drive speed or drive life with regard to GC.
 
maflynn said:
But what exactly is slower by tons mean? Slower then a 5400rpm drive? Would the speed reset by issuing a TRIM command/operation say in windows 7?
Click to expand...

It wont be slower than a 5400 or even 7200rpm drive. But because you will have been accustomed to blazing fast speeds, going back to just over mechanical harddrive levels of performance will feel a lot slower
 
Not saying that this won't happen to me someday but I have a Gen. B MBA w. 128SSD and have had it close to 3GB of empty space on & off since it was 2 months old. My speeds are still very close to as new.

Is the slowing down similar to feeding a rat 2 lbs. of Saccharin a day? In NORMAL use, how long would it really take to slow down? The testings I've seen that demonstrate a slowdown seem to be doing more writing/erasing/re-writing than I may do in 5 years or more.
 
Harrelson said:
It wont be slower than a 5400 or even 7200rpm drive. But because you will have been accustomed to blazing fast speeds, going back to just over mechanical harddrive levels of performance will feel a lot slower
Click to expand...

Good SSDs (Intel etc.) don't go back to "just over mechanical harddrive levels of performance" in my experience. The latency is still low and the random read/write extremely fast. I still contend that the average user wouldn't notice it.
 
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