what to do with a SSD? SSD cache or Boot Drive?

[Newblesse Obblige]

I just bought a 250GB SSD. What should i do: SSD cache or Boot Drive? If Boot Drive, should i put my programs or games to my SSD? Which is better?

I have a 1TB HDD.

[Vasllo]

Boot drive, put all your programs in the SSD (maybe except a few heavy ones you don't need to be as fast) and the remaining space you can use for one or two games, this is what I do. My games mostly go on my 2TB HD, and since most games don't really care that much about an SSD, you'll be fine. I've thought about getting a second one for cache, but haven't tried it yet, not really a high priority upgrade.

 

PS.: Remember to NEVER leave your SSD with less than 10% of it's capacity free, so keep at the very least 20GB free, otherwise you may run into write amplification, degrading your SSD faster and possibly causing slow downs.

[Enderman]

Use it for windows and all your programs.

If there's extra space put some files/documents on it too.

[nonsense42]

15 minutes ago, Vasllo said:

PS.: Remember to NEVER leave your SSD with less than 10% of it's capacity free, so keep at the very least 20GB free, otherwise you may run into write amplification, degrading your SSD faster and possibly causing slow downs.

wait a second... i never knew about this....

 

 

if i have 480gb ssd and have it as a boot drive, but i really don't have any games or documents to fill that space, can i just fill that space with 20 copies of a random 4k movie? (and delete the movie copies if i ever need the space?) or does also cause a problem?

[OmniDyne]

1 hour ago, Vasllo said:

PS.: Remember to NEVER leave your SSD with less than 10% of it's capacity free, so keep at the very least 20GB free, otherwise you may run into write amplification, degrading your SSD faster and possibly causing slow downs.

This generally isn’t accurate. As far as write amplification is concerned, I’d say this is extremely inaccurate. Manufacturers set aside a certain percentage of flash that is inaccessible to the user. This flash cannot be written to by the user; it is used solely by the controller for maintenance and to prevent exactly what you stated: slow downs. This is know as over-provisioning and every modern consumer SSD I’m aware of utilizes this technique.

 

Is filling any storage device to maximum capacity ideal? No. Does it matter? Not really. 

1 hour ago, nonsense42 said:

wait a second... i never knew about this....

 

 

if i have 480gb ssd and have it as a boot drive, but i really don't have any games or documents to fill that space, can i just fill that space with 20 copies of a random 4k movie? (and delete the movie copies if i ever need the space?) or does also cause a problem?

You have nothing to worry about. Use your SSD as you normally would. 

[OmniDyne]

2 hours ago, Vasllo said:

otherwise you may run into write amplification

Write amplification is something that is native to SSDs no matter what you do. You can’t prevent it and it’s even caused by normal SSD on-board tasks, such as wear-leveling. 

[Vasllo]

12 hours ago, OmniDyne said:

Write amplification is something that is native to SSDs no matter what you do. You can’t prevent it and it’s even caused by normal SSD on-board tasks, such as wear-leveling. 

How would the over-provisioned space avoid write amplification from a full drive? AFAIK, the over-provisioned space is supposed to be used to replace eventual bad sectors and keep the capacity of the drive even with the death of sectors.

The only  way I can see that space helping to avoid write-amplification is actually using it's free sectors to write the new data instead of rewriting a bunch of data on an used sector to fit the new data on it, but that would make the inaccessible area accessible and increase the drive capacity, so that can't be it.

I know it's natural for SSDs to have write amplification, like wear leveling, but write amplification from a full drive can be easily avoided, which is an extra degradation of the cells.

 

TL;DR: Could you elaborate how the over-provisioned space avoid write amplification on a full drive? I'm honestly curious.

[NewMaxx]

15 hours ago, nonsense42 said:

wait a second... i never knew about this....

Check the link in my signature. I cover most of these concepts there.

[NewMaxx]

2 hours ago, Vasllo said:

How would the over-provisioned space avoid write amplification from a full drive? AFAIK, the over-provisioned space is supposed to be used to replace eventual bad sectors and keep the capacity of the drive even with the death of sectors.

The only  way I can see that space helping to avoid write-amplification is actually using it's free sectors to write the new data instead of rewriting a bunch of data on an used sector to fit the new data on it, but that would make the inaccessible area accessible and increase the drive capacity, so that can't be it.

I know it's natural for SSDs to have write amplification, like wear leveling, but write amplification from a full drive can be easily avoided, which is an extra degradation of the cells.

 

TL;DR: Could you elaborate how the over-provisioned space avoid write amplification on a full drive? I'm honestly curious.

Check the link in my signature for more details.

 

OP space is reserved space outside OS/LBA/user space, that is not user-accessible. Most modern controllers can use any free space as "dynamic over-provisioning" thanks to aggressive TRIM/GC, although there are a lot of factors to consider/balance in these algorithms. In any case, it's not precisely correct to go by the raw amount of flash in a drive because you have spare area for ECC/RAID, buffers for dies/planes, bad blocks from manufacturing, spare blocks, etc. There's also SLC caching which is the base flash in single-bit mode taking up several times the capacity, and some of this will be in OP space. Ultimately there is a balance between OP and ECC with regards to write amplification (vs. TBW) but more OP definitely reduces WA and wear. This requires some explanation (read my link) but the flash is addressed logically or virtually and not physically so this OP space is shifting, it's guaranteed to be empty and thus available for writes which inherently reduces WA. To understand that you have to see how flash writes and erases (e.g. page vs. block, folding, GC) - for example combining multiple partial blocks into one replacement block. There's also a need to refresh data which includes various algorithms (I cover some in the link). So there's no real easy "tl;dr" but leaving free space on the drive absolutely reduces write amplification, and that's without even getting into the discussion of DRAM.

 

Also, for consumer drives, OP space is likely sufficient from a performance and endurance standpoint, however if you want the best user experience you want to leave some space free for best operation of the drive - OP space alone is not sufficient. (generally, 20% total OP of raw flash is suggested for consumer)

[NewMaxx]

On 3/17/2020 at 10:54 PM, Vasllo said:

PS.: Remember to NEVER leave your SSD with less than 10% of it's capacity free, so keep at the very least 20GB free, otherwise you may run into write amplification, degrading your SSD faster and possibly causing slow downs.

My rule-of-thumb (check my link) is 20% of raw flash or 15% of user-accessible, depending, but it varies widely depending on the drive's design and intended workload. I don't think the world will end with less than 10% free on a SSD but, yes, generally you do not want to exceed 90% drive usage, it will impact performance and endurance, although I think with consumer usage the latter is not a huge problem. Performance depends on the drive - e.g. a DRAM-less SATA SSD will suffer a lot when fuller.

 

Example with 500GB MX500: 512GiB of raw flash, 476.84GiB of user space. 1.20 = 512/x, x = 426.67GiB. 476.84 - 426.67 = 50.17. 50.17/476.84 = leave ~10.52% of the user space free. DRAM-less drives need more OP but usually get more static OP which is better than dynamic, e.g. the BX500 comes in at 480GB not 500GB. If however it came in at 500GB (which it does at larger capacities with QLC) you'd shift to 15% user space free, closer to 25% of raw flash: (476.84)(.85) = 405.31GiB, 512/405.31 = 1.26.