Slow RAID SSD performance

cavemanoc · 25 Aug 2011 at 14:06

I have a pair of Samsung SSD (60ish GB) drives in my laptop and the performance has been degrading steadily over time. I now get:

They are pretty old drives, just pre-dating the trim updates (can't remember the model number) but the write performance was considerably better when I first installed them. I have about 30GB of 120GB let free. Is there any good garbage collection software I can run on a one-off basis to breathe some life back into them? I don't really want to go through the pain of imaging the drives and reformatting etc...

smilertoo · 25 Aug 2011 at 15:53

Raiding SSD disables trim, which means theyll get slower and slower over time. If they dont support trim then all i can think of is dumping the contents to some other storage and erasing them before putting back the data.

cavemanoc · 25 Aug 2011 at 18:05

cavemanoc said:
They are pretty old drives, just pre-dating the trim updates ...snip.... Is there any good garbage collection software I can run on a one-off basis to breathe some life back into them? I don't really want to go through the pain of imaging the drives and reformatting etc...

The drives don't support trim (even individually) - all I really need is a piece of software that does garbage collection on the empty space. There must be something out there by now that does it?

FreeStream · 25 Aug 2011 at 18:19

cavemanoc said:
The drives don't support trim (even individually) - all I really need is a piece of software that does garbage collection on the empty space. There must be something out there by now that does it?

I've not seen anything that does what you ask in RAID I'm afraid, esp for Samsung drives!

Quick and easiest is to clone the drives, wipe the array, run whatever cleaning software you have and then copy it back.

When I was running my 160Gb Intel without trim the process took about 2 hours to copy everything off, wipe it, and copy it back.

cavemanoc · 19 Sep 2011 at 10:22

Just a thought - I noticed CCleaner has a "Wipe Free Space" option that does exactly what I was talking about - effectively overwriting all the empty space on the drive - would this not achieve the same goal as the standard garbage collectors?

Gilbert89 · 19 Sep 2011 at 10:44

cavemanoc said:
Just a thought - I noticed CCleaner has a "Wipe Free Space" option that does exactly what I was talking about - effectively overwriting all the empty space on the drive - would this not achieve the same goal as the standard garbage collectors?

Worth a try then complete a read/write speed test to compare against previous results? It wont take hours.

bradders2000 · 19 Sep 2011 at 11:55

SSD performs best when the NAND hasn't been touched (as in, ever written to).

The only way to get it back to that stage is to Secure Erase the drive (or TRIM those areas). Wiping free space (where TRIM isn't working) will do more harm than good.

So the best thing you can do is take an image, break the RAID, SE each drive, recreate the RAID and then put the image back.

kedge · 19 Sep 2011 at 16:54

smilertoo said:
Raiding SSD disables trim, which means theyll get slower and slower over time. If they dont support trim.

According to research certain ssd's are ideal for raid and have very aggressive garbage collection or Idle Time Garbage Collection (ITGC), which apparently work in a similar fashion to TRIM and helps ensure top performancce levels. Apparently turning off write cache buffer flushing improves certain transfer speeds but research yourselves before committing tests/benchmarks.

cavemanoc · 20 Sep 2011 at 08:41

bradders2000 said:
SSD performs best when the NAND hasn't been touched (as in, ever written to).

The only way to get it back to that stage is to Secure Erase the drive (or TRIM those areas). Wiping free space (where TRIM isn't working) will do more harm than good.

So the best thing you can do is take an image, break the RAID, SE each drive, recreate the RAID and then put the image back.

What's the source for this? Seems counter-intuitive. (A bit that reads zero, reads zero irrespective of how it got there?)

I will run the wipe overnight and see what happens - will be interesting to see.

bradders2000 · 20 Sep 2011 at 09:44

It's the same reason you don't full format or zero fill SSD drives.

When they're unused (erased), the drive knows it and can just write to the NAND. When used (zero filled or whatever), it has to erase before it can write - thus slowing things down.

It's kinda covered here - http://en.wikipedia.org/wiki/Write_amplification#Factors_affecting_the_value

Notice the 'Free user space' bit.

FreeStream · 20 Sep 2011 at 11:30

cavemanoc said:
What's the source for this? Seems counter-intuitive. (A bit that reads zero, reads zero irrespective of how it got there?)

I will run the wipe overnight and see what happens - will be interesting to see.

If it's doing what I think it is doing then it will slow things down.

The SSD keeps track of where the data is, and if there is NAND that it KNOWS is free then it can write at full speed.

Writing zeros to it makes it thinks that space is USED and hence has to wipe it before writing to it.

Secure erasing is the ONLY way to improve SSD performance without trim, and you have to break your array for that.

RAID has always been more effort than it's worth in my mind.