MP 1,1-5,1 Over Provisioning (OP) for Read-Only SSD: does it really matter?

[bosDAW]

This has been asked in the past but nothing within the last 5 years and nothing specific to a read-only drive. So I wanted to post a new thread to ask the question is OP at all necessary for a drive that is used as read-only 99% of the time? Scenario is for a storage drive containing sample (audio) data that, once written/saved, is left alone. The only write operations would be program saves/preset files, templates, etc., which are maybe 1MB at most. Decreased write performance (e.g. adding a new sample library) is NOT a concern. So...

1. SSD/NVMe and overprovisioning (OP) -- Can I safely fill an SSD to 95% capacity or higher for read-only use?

I understand the technical reasons why an SSD will slow down as it gets full and why this may shorten lifespan if doing lots of writes (anandtech review articles, etc.). The best performance will come from leaving more space free in general, but only up to a point and at the cost of the lost space (i.e. absolute best performance may be with 50% empty, but this is simply not practical; 80% may be a more acceptable compromise for average user). Even for the very best drives, things start to slow down as you reach full capacity, but this really seems to be true only for write and not for read. So does this mean I can safely use 95% without experiencing any slowdown in read times? This is assuming a higher quality drive like one of the Samsung 860 SSD or 970 NVMe.

2. Samsung DC SSDs use 6.7% OP -- Should I use the same amount for consumer grade SSD (again, for read-only use)?

If the answer to question 1 is "makes no difference" then this is irrelevant. But it seems that if a company like Samsung uses only 7% OP on its most critical-use drives (enterprise DC SSD lines), then 7% for me is probably more than adequate. Is this true or is this just because they still need to advertise the drive with highest possible capacity and so 6.7% is really a minimum? Or is a consumer drive (860PRO, 970PRO) of lesser quality such that OP should actually have to be higher (>10%).

3. According to Samsung, only DC SSDs and above come with OP from the factory -- This implies that all other SSDs have no OP from factory (i.e. no hidden OP above the listed drive capacity), but can anyone confirm this?

I know that I can look at my Samsung 860PRO 512GB and see 511.xxxGB available for use, so my thought is no hidden/predefined OP. Other people have suggested that a Samsung "512GB" drive is actually designed as a 512GiBi (or ~550GB), and the difference is hidden OP. This seems unlikely to me as Samsung explicitly mentions OP for the DC SSDs, but there is no mention for the consumer drives. If they had OP above the listed capacity, I imagine they would advertise it rather than keep it a secret. So am I correct in assuming that there is no hidden OP for Samsung 860PRO and 970Pro SSDs?

 

[Slash-2CPU]

If the drive is truly read-only, it does not matter. The reality is that on any modern file system on a modern OS, there are always a few writes. Every time you open a file, a write occurs to note last opened time/date.

If you go below a certain amount of free space, the drive will try to level these little writes across blocks. The only way to do this is to move other “stale” or cold data from its current blocks to other ones. That’s write amplification.

For 95% read use case, I’d do 1-2% OP. OS drives, I do 5% OP. If I’m setting up a system for someone I know is a digital pack rat and will load the drive to 100% partitioned full, then I do 7%.

Over provisioning white papers are usually aimed at server/database markets. They will show gains up to 35% OP, but that requires an impossible amount of constant writes for desktop use. Even video editing won’t do what I’m describing. For desktop storage, 1-2% in addition to whatever the manufacturer has hidden from the user is more than adequate.

 

[bosDAW]

That is very helpful! So it sounds like you are saying that anything above 5% is already rather generous, and I should not worry about it. I am sure others may have different opinions, but it sounds like 5-10% is perfectly safe if I wanted to be cautious.

As far as the occasional write (i.e. the other 5% usage), I am assuming that it is the size of the write that is important rather than the number of reads vs writes, but I don't know if this is correct. For example, suppose my drive is 93% full. If I write 5 files every day to the storage drive but all files are <500k, whereas even a single read is 500MB, it is still fair to call such a drive "read-only" (?). And it will not make any real difference as long as I never reach/push it beyond 95% full? I'd think that writing files so small would never pose a real problem in terms of performance, so it is irrelevant.

vs...

Suppose the drive is 93% full, and I want to copy/move one or more 10GB files every day. I would expect to have problems using it like this, and it would no longer be considered "read only" if that were the case.

So in practical terms, I can do as many tiny writes (100-500k file size) to the disk as I want and as often as I want; as long as I do not go beyond ~95% capacity this is safe and will not impact performance in any way for either read/write; or maybe writing such small files really does not matter even up to 99% full?

Thanks so much!!!

 

[Ludacrisvp]

You could always mount it in readonly mode so you'd prevent any accidental writes to it, then only re-mount read/write when you intend to add further data to it.

 

[Slash-2CPU]

Forgot to mention, firmware plays a huge role in how a drive behaves when “cornered” at >95% full. I find higher end drives are much more tolerant of this condition than the budget models.

That said, you can buy a budget model that’s 50% higher capacity for the same price and OP it 7% to come out far ahead for a read-only data storage setup.

 

[AidenShaw]

then I do 7%.

All drives are at least 7% overprovisioned from the factory.

    6TiB      = 6*2^30    = 6,597,069,766,656
    6TB       = 6*10^12  = 6,000,000,000,000

About 7% of the flash is hidden, and is overprovisioning.

 

[bosDAW]

@Slash-2CPU, Is your practice of 1-2% based on the assumption that what @AidenShaw said is correct (all drives have hidden OP no matter what, so 1-2% is really 7 + 2 = 9%), or is 1-2% total OP a safe limit? I already have the drive (Samsung 860PRO 1TB), and I am ok leaving some space free. It is not yet full – I have 220GB left – but I wanted to know if it is ok to add more data and how much. Even going with 5%, as you suggest for an OS drive, means I have 215GB available to use. This should be fine.

Was what I asked about doing small writes (<500k) also correct? In reality, I would probably be writing <5MB total per year for the storage drive. If doing these multiple small-writes, would you then just suggest 5% OP just to be safe? Or maybe another 1-2% more?

@AidenShaw, Is this always true? And for all manufacturers (or at least Samsung)? I was never able to find any info except for a samsung white paper for the DC SSD, but I am not in the tech industry. Without being able to check, it seems very confusing/impossible to know if a manufacturer uses the difference in GiBi for OP but will always sell the product labeled as the lower GB rather than the other way around.

 

[AidenShaw]

@AidenShaw, Is this always true?

There may be some outlier that doesn't quite fit that model - but if the advertised size is a standard TB or GB power of two (256,512,1024) it's a fair bet that the actual flash chips are the same number in TiB or GiB - hence 7% at least. Think about it - the advertised space is in GB or TB, but the flash chips are multiples of GiB or TiB. If the advertised size is lower than the standard power - then the manufacturer has increased the over-provisioning. A 480 GB SSD still has 512 GiB of flash, but more OP.

For example, the 2TB Samsung SSD that's the system drive on my home workstation reports:

Actual Size : 2048.408 GB 1907.729 GiB 4000797360 Sectors​

This means that it has 2048 GiB - 1907 GiB = 141 GiB of over-provisioning. (In practice, it might be slightly less because the SSD controller may allocate some space for its own use.)

SSD Over-Provisioning And Its Benefits | Seagate US

Question - Proper 970 EVO (1tb m2 ssd) Setup: Trim, Over Provisioning, etc

Hi, I am using the drive in title as a media cache drive for adobe premiere video editing + a few simulator games installed (DCS world, xplane, star citizen) which really need the SSD. What is the proper setup beyond plug and play and format to NTFS? 1. Trim enabled - yay or nay? 2. Is...

forums.anandtech.com

Also note that if TRIM is enabled, then any unallocated space in the filesystem acts as additional over-provisioning.

 

[bosDAW]

Ok, so my drive is listed by Samsung as "1TB" in size, with 1024GB spec capacity. Reporting on the drive in my system shows it as 1.02 TB (1,023,865,569,280 Bytes). Does this mean it is actually 1024GiBi x 1.93GB/GiBi = ~1099GB and the factory OP is 1099GB - 1024GB = 75GB? TRIM is enabled.

If that is the case, leaving an extra "5%" of visible space gives 5% + 7% = 11%.

Or the long way: 0.05 x 1024GB = 51.2GB user OP + 75GB factory OP = 126.2GB total. Converting back to GiBi, 126.2GB x 0.93GiBi/GB = ~117GiBi total OP/1024 GiBi x100% = ~11.5% so seems right. Or am I getting this all mixed up?

Even if my math is wrong, any extra space I leave free from the drive size my system sees as 1.02TB will be extra OP above the factory 7% (75GB). The 5% user OP is safe because it is actually more like 10% total and so plenty for a system (OS) drive. For a read-only drive used as described, 5% is probably more than enough and so could even be a little less (say 1-2% according to @Slash-2CPU + 7% factory = 8-9% total and still pretty safe).

Bottom line, "5%" of a "1TB" drive gives at least 50GB user OP. What I asked about doing small writes (<500k)...
"in practical terms, I can do as many tiny writes (100-500k file size) to the disk as I want and as often as I want; as long as I do not go beyond ~95% capacity this is safe and will not impact performance in any way for either read/write; or maybe writing such small files really does not matter even up to 99% full?" Still correct?

 

[AidenShaw]

Don't worry about OP. Just make sure that TRIM is enabled, and leave some free space (TRIM'd free space is equivalent to OP space). If you do feel the need to (or accidently) fill the disk, just restore the free space as soon as convenient. In any event, you'll always have the 7%.

Your drive is rated at 1,200 TB of writes - calculate how many years it will take you to reach that.

 

[bosDAW]

Sorry, I made an edit while you were posting a reply. I would be curious to know if I am doing the math correctly to understand the conventions, but it sounds like the conclusion of my last paragraph in the previous post is correct (and essentially what you just said now). The small files that will be written are insignificant. So leaving 5% just to be sure (which is really 11%) is more than adequate.

 

[AidenShaw]

So leaving 5% just to be sure (which is really 11%) is more than adequate.

If you want to waste 5% of your drive - sure. Did you calculate how many years that it will take you write 1.2 petabytes?

You have basically a read-only drive, and you're going to provision it like it's a read/write database.

In your situation, I'd stay with the default 7%, fill the drive with a partition, and try to keep 5% to 10% free (TRIM'd) space.

Free (TRIM'd) space is just as good as OP space - but gives you the option of using it in a pinch - and having it revert back to "OP" space when you delete the files and get back to 5% to 10% free. It's win-win.

 

[Slash-2CPU]

The OP I refer to is in addition to what the manufacturer hides from the user.

While trimmed free space is as good as OP space in theory, the reality is that users tend to fill drives to 100% of what you partition. Even a tech savvy user can still have an app, OS, or OS update puke several dozen GB or more of data onto the drive.

The additional reality is that, in my experience, drives tend to still function reliably at 95-100% full, but the performance drops to somewhere between half of normal and 1990 floppy disk. Not exaggerating. I’ve had write latencies measured in seconds per IO with near full SSD’s. Not IOPS, but SPIO.

It’s not about write endurance. It’s about maintaining performance that doesn’t go to absolute garbage where you get to enjoy watching the delete command to reclaim that upper 5% take 20 minutes.

Lastly, if your drive is TLC or QLC, it most likely uses a SLC mode write buffer. As the drive fills up, that goes away. Not relevant for a read-only setup, but another good reason to have a little additional OP in user land.

 

[bosDAW]

@Slash-2CPU, the Samsung 860PRO is listed as 2-bit MLC, if that changes anything. Your initial suggestion for a read-only drive was 1-2%, but it seems you are now saying it is still better to add 5% free space on top of the hidden OP. Does it have to do with the small write operations I described, or is the 5% just a best-practice to ensure good performance regardless of drive type; TLC, MLC; etc?

I have no partitions on the drive (i.e. single partition), and I think 5% is easy to do. Most libraries are somewhere between 1-15GB, and I might be tempted to go over the suggested OP by a little bit, but it should be easy to stop with 40-45GB still left over.

Just to be clear, pretty much all of the content will be read-only sample data except for maybe a few MB of saved presets. So for me, getting the drive to the point of "filled to the brim" would in reality look like ~980GB read-only samples + 10MB of small read/write files. Beyond that, I would have to get a new drive to accommodate more libraries anyway. Is that reasonable in terms of maintaining performance and reliability as well as endurance?

 

[AidenShaw]

If the drive has been used, be sure to TRIM any extra space you set aside for OP.

You should have purchased a 2 TB drive....

 

[Slash-2CPU]

For 860 Pro specifically, 1% additional user OP is fine for read only. I would expect that drive’s more powerful controller and top notch firmware to handle 99% gracefully.

5% is for cheap, off brand TLC and QLC drives.

Overall, as AidenShaw indicated, you may be better served with a cheap 2TB drive with 5% OP. The 860 Pro is meant to be able to handle a lot of writes, and you paid extra for that. TLC and QLC are almost ideal for the use case you’re describing.

 

[bosDAW]

Got it! So my setup is fine, 1% is fine, except it might not be the best use of the drive for the money spent.

Maybe the 860Pro would be better served as a backup to be written and re-written multiple times. And something like the 860Evo could be swapped in as the better choice for sample storage. I had this backwards, thinking that a backup drive [almost by default] should be something inexpensive with larger capacity. But after this discussion, I realize it is more a question of how often it will be written. And having to add more OP with a cheaper drive is not a big deal because the cost/GB is so much lower that you still get more than enough free space even if you end up having to buy a drive twice as large.

A sample drive (95% read only) --> works fine with TLC or QLC (e.g. 860Evo is perfect, no reason to waste $ on Pro)
A backup for a sample drive --> probably does not matter, since a 95% read-only disk does not need to be backed up very often, maybe once a month (e.g. any QVO is perfect)

System drive and/or scratch drive --> frequent read/write, MLC is put to good use
A backup for system drive --> daily/weekly backup, MLC is put to good use

 

[tsialex]

Did you ever used a macOS drive not read-only that have just 1% free? Ever looked at the Console? Try it.

Never use a drive that is not mounted read-only full, macOS goes crazy with notifications to you and to logs if you use a drive with less that 5% free space. Another thing, while the logs are being saved and the notifications pop-up, your disk access is deadlocked.
[automerge]1587545857[/automerge]
Btw, there are dozens of reports that Samsug QVO drives don't work correctly with Mac Pro when installed internally or on PCIe SATA cards, just work over USB.

 

[bosDAW]

Do you agree/disagree with comments regarding 1% free space as safe for a high-end drive used as read-only? Or in your experience do you leave 5% free no matter what type of drive or how it is used?

Everyone seems to have a different preference, and maybe it depends on the drive and the OS, but this makes it difficult to decide. Some people suggest 70% max; while this may be true for best possible performance, it is not really practical for storage.

I have never actually had a working drive more than 60% full anyway, so I never really knew or thought about OP before and only now starting to learn about it. A sample/read-only drive is different because, forgetting about performance, libraries are so large that you have to check if you have enough space simply for one to fit. And every time you are looking at a new library, you have to decide what the acceptable limit is on filling a drive versus buying a new set of larger drives, getting an expansion card, deleting or archiving data to free up space, etc.

As an example for me, I wanted to know if my drive that is currently at 85% will be happy filling up to ~95% or if I should be limiting it to 90%. The difference would be between being able to get a new library or having first to get a new drive, which may be more than the cost of the library. And if I need to move a few things onto another drive to the point of also getting close to 90% full, adding a single new library may result in having to replace multiple drives to have room for everything.

So it is less about being stingy with space and more just understanding what is a safe limit for read-only. 10% free space seems reasonable, but across 2 or 3 sample drives that may be 1-2TB each, this can add up to 200-600GB total of "lost" space. And with large libraries, it is unlikely that I'll be able to land right at the 90% mark, so a drive may stay at 85% full and I lose that extra 50GB as well.

And thank you for the note about Samsung QVO!

 

[AidenShaw]

Why haven't you realized that the default is always at least 7%? Why are you talking about 1% and 5%?

Use the default - but make sure that it's a virgin drive. If it's not virgin, then make sure to do a whole disk TRIM before partitioning. (AKA as "secure erase")

Your use case is basically read-only - the 7% default is fine for you. No need to add a few more percent. You're making a mountain out of a molehill - you're worrying about nothing.

If you have a busy read-write database - think about overprovisioning. If you have a read-only sample database - worry about other things. And, if you have a busy database - you'll probably be looking at high write load SSDs that already include strong over-provisioning - like some Intel PCIe SSDs that I have that have 256 GiB of flash and expose that as 200 GB after OP.

LOL - the following picture was inserted into this post by my cat walking across the keyboard. Seriously - it's cat content.

* Fo

Stay safe.

https://www.huffpost.com/entry/rainbow-masks-poland-to-fight_n_5ea1aa5dc5b6f5350a34c11a

Is it possible that my cat is gay?

(Yes, I'd copied the mask photo to some friends - but somehow the cat walk pressed the right keys to add it here.)

 

[bosDAW]

Decreased performance for audio means distortion or drop outs, which are immediately noticeable. From the documentation of one of the prominent companies that release sample libraries:

"Free Disk Space: We recommend keeping a percentage of disk space free on the drive where libraries are installed. Our tests have shown that the speed at which data can be read from a drive decreases as disk space is used up. Try to keep 30% of each library drive empty to avoid reduced performance, which can drop by half with the drive 90% filled."

It sounds like maybe they have this completely wrong, but you can see why I came to the forum with so many questions. Either way, I feel like they make it difficult for their customers when a single library averages ~60GB. At least they don't also try to sell SSDs.

Maybe your cat was just reminding me there are things more important than OP!

 

[bosDAW]

BTW Is there any validity to the notion of running Disk Utility>First Aid on a system drive to force a trim? Does the "trimming unused blocks" operation at the end work in any way similar to a "secure erase", so if trying to reset a drive or do a fresh OS install, could the drive be erased first and then trimmed with First Aid to improve performance?

I know there is no way to do a secure erase natively on a mac, and Samsung Magician works only with Samsung drives. I have access to a PC if that is really the best way for someone with little experience, but I also have an Apple branded Toshiba drive. TRIM has always been enabled on the Apple drive, but I thought it might benefit from a fresh OS install to eliminate any digital clutter.

 

[AidenShaw]

"Free Disk Space: We recommend keeping a percentage of disk space free on the drive where libraries are installed. Our tests have shown that the speed at which data can be read from a drive decreases as disk space is used up. Try to keep 30% of each library drive empty to avoid reduced performance, which can drop by half with the drive 90% filled."

This is true for most (all?) modern spinners - there are more sectors per track on the outermost tracks, so more sectors pass under the heads per rotation. As the drive fills (assuming that outer tracks fill first) the read/write speed drops.

​

Read speed on SSDs should be nearly constant as it fills. Write speeds for large writes on SSDs may suffer if garbage collection is necessary.

 

[bosDAW]

I still do wish there was a way to do trim and/or "safe erase" for mac users, but it looks like this has been a commonly asked question for many years, so probably not. And Samsung likely has no reason to make Magician for mac OS.

thanks @AidenShaw for all your help. Much appreciated!

 

[AidenShaw]

I still do wish there was a way to do trim

The command 'fsck -fy' will trim all of the unused space in filesystems. It won't trim the OP space.

On Windows, Magician creates a bootable thumb drive to actually do the secure erase procedure - if you're dual booting you could try booting that thumb drive. Or connect the drive to a Windows system and create the thumb drive.