new SSD question

[polonyc2]

I have a 256GB Falcon SSD drive...I've heard that you should always leave 20% free space on the drive as to not fully use up the SSD to prevent performance degradation...does this refer to leaving 20% free from the full stated capacity of the drive or just from what is left after Windows recognizes the drive?

meaning if I have a 256GB SSD do I count 20% of 256GB or 20% of 238GB? (238GB is what is shown when I'm installing the OS)

 

[TehQuick]

It's not written in stone, even that 20% is an approximate number, not exact science... so it's up to you, really.

 

[InvisiBill]

It's the same thing either way. The difference in listed sizes is due to gigabytes vs. gibibytes. 256,000,000,000/(1024^3) = 238.42GiB. Regardless of which method of measuring you use, 20% of the drive is still 20% of the drive. 20% of 256,000,000,000 bytes is 51,200,000,000 bytes. 20% of 238.42GiB is 47.68GiB. 51,200,000,000/(1024^3) = 47.68.

According to Anand, Intel really does use the full number of gibibytes (__x1024^3), but advertises the capacity in gigabytes like hard drives do (__x1000^3) and uses the difference as built-in spare area. My "80GB" would actually contain 85,899,345,920 bytes, but Intel only makes 80,000,000,000 bytes available to the user, leaving the other 5,899,345,920 bytes as spare area. The 80,000,000,000 bytes works out to the ~74.5GiB seen in Windows. This gives about 7% spare area even if you don't leave any free. This perpetuates the confusing GB vs. GiB stuff, but it makes SSDs behave the same way as HDDs (since people are mostly used to that now) plus it allows them to easily build in spare area. I have no idea if the Falcons are the same, but you may already have some working room built in as well.

 

[Sathsayin]

I think that he means do I need to either save 20 percent and not write to it ? IF so which number do I use 238gb or 260gb. IF that is the case then Do I need to stop at 195 or so on a 238gb and 210 gb or so on 260 gb....

I think that is what the op was asking. If so.

Then I would say 210 or so as you can only use what windows recognizes. Buying a certain size disk even solid state is not going to be full speced size.

Refer to this sticky!
Why is my hard drive smaller then the advertised capacity?
http://www.hardforum.com/showthread.php?t=1347640

With that being said. you need 20 percent supposedly avaialble in order for the disk to have enough room to erase rewrite then save your data..... so 20 percent of 238gb would be around 47.6gb I'm guessing. 196 or so is where I would stop if you want 20 percent.
Although this isn't set in stone. I wouldn't go over 15 percent. Once you do even erasing it will not get you performance back untill you do a lowlevel format.....

 

[polonyc2]

I think that he means do I need to either save 20 percent and not write to it ? IF so which number do I use 238gb or 260gb. IF that is the case then Do I need to stop at 195 or so on a 238gb and 210 gb or so on 260 gb....

I think that is what the op was asking. If so.

With that being said. you need 20 percent supposedly avaialble in order for the disk to have enough room to erase rewrite then save your data..... so 20 percent of 238gb would be around 47.6gb I'm guessing. 196 or so is where I would stop if you want 20 percent.
Although this isn't set in stone. I wouldn't go over 15 percent. Once you do even erasing it will not get you performance back untill you do a lowlevel format.....

thanks...that's exactly what I wanted to know

so if I fill my SSD to capacity even running Wiper/TRIM will not get me my full performance back?...only way to do that is by doing a full erase of the drive using Diskpart or some other method?

 

[InvisiBill]

thanks...that's exactly what I wanted to know

so if I fill my SSD to capacity even running Wiper/TRIM will not get me my full performance back?...only way to do that is by doing a full erase of the drive using Diskpart or some other method?

I have never seen anything about needing a low level format to get performance back. Every test I've seen contradicts that fact actually.

Read Anand's whole SSD Anthology. It'll teach you exactly why SSDs behave the way they do. The performance degradation is due to the fact that NAND flash can't be overwritten like a platter HDD, it needs to be erased then written. When the drive is brand new, all the pages are clean and can be written to nearly instantly. Unlike a HDD, the SSD's controller is smart enough to remap data locations for performance and longevity (i.e. sector 0 isn't necessarily mapped to the first page on the first flash chip). Once you've written enough data to your new SSD, all the pages eventually contain data. Just like deleting a file doesn't actually delete the data off a platter HDD (which is why we have stuff like DBAN to overwrite the entire drive), deleting a file doesn't actually remove the data from the page in the SSD. The SSD's controller doesn't know which pages hold valid or invalid data. It just perpetuates whatever data is in that page until the OS instructs it to write other data there. When all of your pages get filled up with data (current files or deleted data), every single write on the drive will require overwriting existing bits. As previously stated, NAND can't do overwrites, so you actually have to cache the valid data in that block, erase the block, then write back the previous valid pages plus the new pages of data. This obviously takes longer than simply writing data to an empty page.

TRIM allows the OS to tell the SSD when it's deleting a file. This allows the SSD to erase those pages during its normal maintenance, rather than just perpetuating those bits until the OS tells it to overwrite them. This allows the SSD to keep more pages erased, which means you're more likely to be able to do an instantaneous write (as well as rewriting fewer invalid bits, meaning less wear on the flash).

All the TRIM tests I've seen show that the drive retains performance nearly identical to a new drive. I've never heard of anything like a low-level format that somehow makes the blocks "more erased" than TRIM/Wiper/etc. If you don't have a tool like that available for clearing out only the unused blocks, then the ATA Secure Erase command (via a tool like HDDErase, hdparm, Parted Magic, etc.) will erase all blocks on the drive. This is what people did previously on SSDs - they'd make a backup of the data on the SSD, erase the whole thing, then restore their data back to it.

 

[polonyc2]

All the TRIM tests I've seen show that the drive retains performance nearly identical to a new drive. I've never heard of anything like a low-level format that somehow makes the blocks "more erased" than TRIM/Wiper/etc. If you don't have a tool like that available for clearing out only the unused blocks, then the ATA Secure Erase command (via a tool like HDDErase, hdparm, Parted Magic, etc.) will erase all blocks on the drive. This is what people did previously on SSDs - they'd make a backup of the data on the SSD, erase the whole thing, then restore their data back to it.

won't the Diskpart 'Clean All' command do the same thing as HDDErase?

so you're also saying that it doesn't matter if the drive gets filled to capacity as long as TRIM or Wiper is used?

 

[InvisiBill]

won't the Diskpart 'Clean All' command do the same thing as HDDErase?

so you're also saying that it doesn't matter if the drive gets filled to capacity as long as TRIM or Wiper is used?

As far as I know, Diskpart will simply wipe the partition table, not erase all the data on the drive.

Also AFAIK, TRIM and eraser utilities do just as good a job erasing as anything else. I've heard that Wiper may need to be run several times to get everything. If the drive gets full, it will have less spare area to work with while doing writes. Some SSDs will use free space as spare area until its been written to once. Once it's been written to, then it no longer uses that space as spare area even if it gets erased. Other SSDs will dynamically use any free space.

TRIM allows the unused blocks to be erased ahead of time, meaning that you should have more clean pages available for immediately writing, which means it shouldn't need to use the spare area as much.