I am fortunate to have a dedicated FSX rig with my OS and FSX on two separate SSDs. Win7 sits on a 65gb drive with usually about 8gbs of free space always available. FSX is on a 250gb drive and has currently about 60 gb free. My question is, do SSDs have to maintain 30% free space to maintain efficiency, like a standard Sata HD, or can I fill more or less the entire SSD without any loss of performance? Advice and help always appreciated fellas, cheers.

10% free space for SSD give or take, after that your SSD will not be as efficient. I keep mine at 15% free space just to be sure.

I agree with Hypodermic, 5-10% is all that is needed for essentail disk/file maintenance. There is no fall off in performance as it fills up.

Regards

pH

I agree with Hypodermic, 5-10% is all that is needed for essentail disk/file maintenance. There is no fall off in performance as it fills up.

Regards

pH

 

Indeed, filling up your SSD over 90% of its capacity is like trowing a monkey wrench into your system.

OK, more or less what I thought, thanks Alain, Peter appreciated...

I'd like to know where these 10-15% free space recommendations come from.

 

Most SSDs already have non-addressable free space in the flash memory array for the firmware to use in its internal wear-levelling routines. Keeping 10% free is a throwback to platter HDD systems (related to defragmentation requirements that do not apply to SSDs). I've not yet seen a credible explanation as to why an SSD needs to keep a certain amount of addressable free space available to remain efficient.

I've not yet seen a credible explanation as to why an SSD needs to keep a certain amount of addressable free space available to remain efficient.

 

TRIM allows free space in a partition to be treated as spare area. No free space means less spare area. Take a look at this part of AnandTech's SSD Relapse article (read the whole thing if you have the time). If you look at a few of Anand's SSD reviews you'll see he benchmarks the drives after completely filling them, and performance can change by a lot. The implications vary between drives, for example SandForce-based drives don't deal well with being completely written to.

 

All that said, I also don't know where the 10-15% free space number comes from. Personally, I just don't let my drive fill up.

 

Cheers,

 

Mike

Unless wear levelling actually moves already pre-existing data to a new location as well as writing new data to free space in an equal wear levelling way, then filling an SSD to almost full can't be a good idea as that small area of space left is going to continually get a battering.

 

I was under the impression that once data (which was never going to change again, such as a game level for instance) was written to the SSD it stayed in its bit of flash memory until the data changed, so if it never changes, it never moves, if it never moves then any free space that is left will continually get worn away while the rest of the memory stays in pristine condition because reading data on an SSD does not wear the memory out, only the actual writing of data to a flash cell causes wear. I leave my drives with about 20% free space just because of this.

 

@Andy--Wear-levelling does indeed move "static" data (static as seen from the operating system's perspective) around on the array so that writes are more or less evenly distributed across the flash NAND array. Data locations as reported by the SSD are mapped virtual locations, and not a physical address in the array--so repeated writes to the same specific "disk" address on the SSD are not being made to the same physical flash array address. Most, if not all, SSDs have some extra flash memory in them above and beyond the addressable limit that is used internally by the SSD's controller hardware to move data around in the background.

 

@Mike--slowdowns without TRIM are caused when an SSD has had all its flash written to at least once. Note that this can be caused by filling up the drive, but that it does not necessarily entail filling up the drive. For example if you have a 160GB SSD, and write a 1 GB file, then erase it, and repeat that process 160 times, all 160GB of the flash will have been written to once without ever coming close to filling the SSD. Without the SSD controller being made aware of which file system pages have been released by the OS (this is what the TRIM command does), the controller cannot clear the empty pages associated with deleted files ahead of time (done in the background by the SSD controller). Flash memory must be physically placed in a cleared state before being written to, so a write operation to those uncleared pages then requires the entire 128-page block occupied by that page first be read, then erased, then all 128 pages written back, instead of just writing out one 4K page as happens when the controller sees that the target page is already cleared and ready for an immediate write. That "block read-block erase-block write" process slows writes on the drive way down, and will continue to slow it down even when space is subsequently freed up by deleting files. Note that this has nothing to do with how much free space windows thinks remains on the drive.

@Andy--Wear-levelling does indeed move "static" data (static as seen from the operating system's perspective) around on the array so that writes are more or less evenly distributed across the flash NAND array.

 

Thanks Bob for the explanation I wasn't aware of that, I didn't think the algorithms were that smart, I am glad I was wrong.

So guys, do I need to allocate 'free' space to the OS drive as well as the FSX drive?

"Allocate free space"?

 

What does that mean?

 

I don´t "allocate" anything on my SSD´s, but then again, I´m not American or English, so I don´t know the lingo.

 

 

If you have 2 SSD´s then my understanding is that you keep 10% as free space, right?

 

Simple, or complicated??

 

:Thinking:

So guys, do I need to allocate 'free' space to the OS drive as well as the FSX drive?

 

Honestly, I see no compelling reason to do that--assuming that you are running Win 7 and have TRIM enabled.

 

If you were to see a noticeable slowdown (very unlikely IMHO), fixing it would be as simple as taking some stuff off the drive.

Honestly, I see no compelling reason to do that--assuming that you are running Win 7 and have TRIM enabled.

 

If you were to see a noticeable slowdown (very unlikely IMHO), fixing it would be as simple as taking some stuff off the drive.

 

Hi Bob, thanks for the info, very helpful. Although I am ignorant about TRIM being enabled... what is that?

What is TRIM?

 

http://www.bit-tech.net/hardware/storage/2010/02/04/windows-7-ssd-performance-and-trim/1

 

Instersting stuff!