SSD and HDD speed with respect to % capacity used...

[Caveman]

A few questions regarding the subject...

Assumption is SDDs and HDDs both slow down when getting full... I seem to recall that HDDs start to slow at the 50% full mark and head rapidly downhill from there (maybe half speed at 90% full)...

How about SSDs?

What is their speed vs capacity used characteristic?

I assume there are some general rules of thumb here on NTE space to use on drive of capacity "X"...

Question on a related note: 500 GB SSD is divided into 2 partitions: 150 GB and 350GB. The 150GB portion is 90% full (135GB of 150GB) and the 350GB portion has only 5% capacity used (17.5GB of 150GB)... Does the "speed rules of thumb" asked about above relate to the entire capacity of the drive or are they on a per partition basis? In other words, when files on the 150GB partition are accessed, will they be VERY slow relative to the other partition?

 

[razel]

HDDs slow down sequential speed and access time from full speed to 50%.

Modern SSDs will only slow down write speed when full if you abuse-ly punish them. Read speed is unaffected which you do 75% of the time. No, there will be no write speed difference between a full partition and a empty partition on the same SSD. This is primarily because a disk is strictly sequential structure while SSDs can be dynamic. Because of this when your 150GB partition is full, it still can use empty NAND blocks from the 350GB. If your 350GB is full, it still has reserve NAND blocks to use.

Essentially it knows that you want two partitions and the size of each. But it doesn't pre-allocate or assign it to each partition until you begin writing. So empty blocks are available to both. Awesomely smart isn't it?

My explanation is oversimplified and may not even be correct for all SSDs. How they really get it done, I'm sure is a trade secret, but you get the idea.

 

[Cerb]

There is no magical slowdown at some % full. I ran my old 1TB system drive over 90% full for multiple years, and it performed almost as fast as new. I didn't exactly run DBs on it, though. Peak performance will be lower, but that happens with mere 25%, or less, usage, today.

If you don't have excessive fragmentation, and have decent amounts of contiguous free space, how full it is won't make much difference, in % terms. Every modern FS scatters files about the drive, making the sequential synthetic numbers near the platter edge meaningless, once you put any substantial amount of data on it. The absolute free space on modern drives is simply enormous, compared to day to writing (IE, you aren't writing much more on a 2TB HDD than when you had a 160GB HDD, you can just fit more static data), and generally gives the OS plenty of room to work in.

With an SSD, without TRIM, it will always be 100% full, after some use. With TRIM, it will vary. But, just get an SSD that doesn't bog down too badly, and recovers well, and you'll be alright. If you need the space, use it. If you don't, clear it out so it can be used faster and more efficiently in the future.

That is the face of a nearly full SSD, struggling to manage efficient access to my files, and not slow my PC down to a crawl ^_^. I've been lazy with my game library's bloat, and need to do some housekeeping. Nonetheless, it's a good example of what happens in real world use, with plenty of idle time, rather than the torture that reviewers like to put them through. It's a 480GB M500, on a B85, with the MSAHCI driver. Its lifetime WA has climbed to 4.3, from 2.8 before I allowed it to fill up like that, so there are consequences of note (IE, current WA is surely >5). But, between TRIM and idle wear-leveling, it manages fine. 4K@QD=1 write has clearly suffered the most (due to WA needs?), but is still respectable, and not noticeably slowing anything down.

Any changes from space used only apply to the used space of the whole SSD.

 

[Deders]

What's all this about HDD's slowing down when 50% full? Granted HDD's can be 50% slower near the end of the disk than at the beginning but that's why I partition my disk so that the programs are all on the first half or less of the disk.

Not only does this keep all the programs in the same area, meaning the head will never have to travel all the way across the platter no matter how defragmented it is. Plus it will always (in my case) be able to sequentially read over 120MB/s for programs.

Even if the partition is nearly full, it does not get slower. I have real time disk monitoring software that tells me exactly how many MB/s it is doing at any time.

I have noticed unpartitioned drives get slower when they are full bu tthat is because there is no space to put anything at the beginning of the disk.

 

[Elixer]

It all depends on where the data is for HDs, there are no HDs that have the same speed across the entire platter since the way physics works.