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LZ4 vs. ZStd

Western Digital Drives - The Preferred Drives of FreeNAS and TrueNAS CORE

mpfusion

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I'm about to create a new pool (TrueNAS-12.0-U1). There doesn't seem to be much info about the different choices and which one to pick. The data is a mixed bag of everything. Small files, big files, source code, incompressible files, VMs, …

LZ4 or ZStd? How to decide?
 

Chris Moore

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kspare

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so zstd maybe better for file servers/file storage, lz4 better for terminal servers?
 

Chris Moore

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so zstd maybe better for file servers/file storage, lz4 better for terminal servers?
More like cold storage vs hot storage. If you don't mind it being a little slower to access, and the difference is not massive, the ZStd appears to offer better compression. If you are interested in fast access to the data, LZ4 appears to still be the fastest answer.
I have only begun to investigate, and it is fairly new, so I am not claiming to have the definitive answer.
 

kspare

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More like cold storage vs hot storage. If you don't mind it being a little slower to access, and the difference is not massive, the ZStd appears to offer better compression. If you are interested in fast access to the data, LZ4 appears to still be the fastest answer.
I have only begun to investigate, and it is fairly new, so I am not claiming to have the definitive answer.

Let me know if you need any help or compare notes. we're going to try some terminal servers on zstd level 3
 

mpfusion

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Thanks for the answers so far. I guess I'll stick with LZ4 then, as compression is not paramount and I'd rather avoid any performance degradation just to save a few gigs.
 
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kspare

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so far i'm seeing an improvement in compression. 1.25 to 1.4-1.5 quite signifigant.

I'm not seeing much for performance loss, infact i'd say we've gained! it's looking good.
 

kspare

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once I migrated vm's from all 3 storage servers to my test server, we saw a compression ratio of 1.36.....fairly significant from 1.25.

This represents about 77 terminal servers and close to 700 users. so we'll see how things run tomorrow. but it looks good so far.
 

Scharbag

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It has also been said that since the CPU is soooooo much faster than even SSDs, the bottleneck will not be the inline compression but rather the storage infrastructure. So that is promising.

Cheers,
 

Chris Moore

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It has also been said that since the CPU is soooooo much faster than even SSDs, the bottleneck will not be the inline compression but rather the storage infrastructure. So that is promising.
For most systems, using compression actually makes them faster because of the speed factor you describe actually reducing the amount of work the mechanical disks need to do because the data is smaller. The comparison testing that has been done so far does show a compression benefit, but a small speed loss and I am not sure how noticeable that will be in practice because most people have a small enough pool of disks that their mechanical storage is still the slowest part of the chain and the absolute speed limiting factor. That said, if the data is smaller due to compression, the time to write (or read) it to and from the disk might be a little less. Will it be enough to notice a change for the user? In a large implementation it might save some space on disk. I plan to give it a try. I just wish it had been released a couple months earlier because I just finished bringing a new server online and the initial data load is already done.
 

kspare

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We made 2 changes.

1 updated to U1 and used the new compression. our performance is actually not as good. so i'm still evaluating.
 

Herr_Merlin

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We made 2 changes.

1 updated to U1 and used the new compression. our performance is actually not as good. so i'm still evaluating.
I'd did not have difference with lz4 vs zstd7 which is strange. Even more so the data wasn't compressed with zstd7 at all..
Wanted to try it out to see for myself on a test system.
Performance with both was equal. Pool usage with zstd higher plus UI showed a ration of 1.0...
Any ideas?
Want to replace the max gzip pools with zstd to gain a bit more speed on the archives..
 

mpfusion

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Ok, I was curious and created a 2nd pool with zstd (default level, 3) and replicated the pool. Space savings are 5.7% compared to LZ4. As I haven't used the 2nd pool, I cannot tell anything about the performance, though.
 
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Something I'm trying to wrap my head around is if you change the compression option for a dataset that already has many files inside, do the existing blocks get re-written eventually (under-the-hood maintenance) with the new compression method? What if you modify an existing file? Does the copy-on-write write the new blocks with the updated compression method, or with the file's / block's original compression method?
 
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ornias

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Whoops, I totally missed this thread...
Here my cents:

That literature isn't that great, because the ZSTD implementation in ZFS is not directly comparable with native ZSTD, performance wise.
I would suggest looking at my (older) performance tests on Linux.
older numbers (slightly bottlenecked tests):

Full latest test results by me:

And the followup by Allan Jude:


Short answer is that ZStd compresses more, but slower. LZ4 is faster.
Thats a simplification, because in a lot of cases the compression algorithm isn't the bottleneck.
Actually both me and Allan had/have trouble getting good numbers due to there being multiple bottlenecks when it comes to testing ZSTD within the whole ZFS stack.

Depending on things like recordsize and write pattern, both are perfectly capable of saturating more than a 10gb/s connection on a not-too-fast CPU (part of the threads from a 1700-non-k)


If you don't mind it being a little slower to access
It's actually the writes that are most affected by going from LZ4 to ZSTD, not the reads. As ZSTD is designed to be a LOT faster in decompression than it is to compress things. Unless you mean "access times", but I don't think we have specific numbers for it except iops.

the difference is not massive, the ZStd appears to offer better compression. If you are interested in fast access to the data, LZ4 appears to still be the fastest answer.
Thats an oversimplification because just because LZ4 is faster in most usecases, doesn't mean most people are actually pushing enough throughput to actually saturate their (spare) CPU (cycles) with ZSTD.

The correct answer would be something like:
"If you are running less than a modern 6 core intel CPU, with SSD based pools AND want to push multiple GB/s (thats bytes not bits) of either reads, writes or read-writes, ZSTD is not going to cut it"

Let me know if you need any help or compare notes. we're going to try some terminal servers on zstd level 3
Maybe let me know if you need help. Okey just kidding ofcourse :smile:
- What are the server specs and the expected load (both writes, reads and iops) on said server?
- What are your expected dataset settings besides zstd? (primarily recordsize)

If it's mostly low blocksize reads, be aware a significant performance improvement to ZSTD is made in the latest 1.4.7 release.
I've just submitted the PR to said ZSTD version for ZFS yesterday:

Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz - 24 2TB - LSI 9207 - Intel 750 NVe - 64GB - Celios 10GB
is it the system in your signature?
In that case it's somewhat comparable to the system I used in my performance tests (except disks, performance tests where done using ramdisks).
You would really need to push your 10GB network card to its knees before you are going to be affected by performance limits of ZSTD in most usecases.

Thanks for the answers so far. I guess I'll stick with LZ4 then, as compression is not paramount and I'd rather avoid any performance degradation just to save a few gigs.
Thats why you shouldn't rely on generalised statements, all the answers do not account for your personal setup. Chances are you never would've had any performance degradation at all or would even have had a performance improvement (if you are bottlenecked by your disks and have lots of sequential data)


It has also been said that since the CPU is soooooo much faster than even SSDs, the bottleneck will not be the inline compression but rather the storage infrastructure. So that is promising.
That would be an oversimplification the other ware around.
With a 25Gb/s network card + 1 NVME SSD, it's possible to create a CPU bottleneck with a modern consumer intel 6-8 core CPU.
With harddisks you would be looking at A LOT of harddisks, but even then it is technically possible.
That being said: Those are not normal loads for most of us users, besides peak-load most important is the average load and spread of said load over the day, combined with peak expected load. It's quite likely that you wouldn't hit a CPU bottleneck, because you still need data to bottleneck on ;-)

For most systems, using compression actually makes them faster because of the speed factor you describe actually reducing the amount of work the mechanical disks need to do because the data is smaller. The comparison testing that has been done so far does show a compression benefit, but a small speed loss and I am not sure how noticeable that will be in practice because most people have a small enough pool of disks that their mechanical storage is still the slowest part of the chain and the absolute speed limiting factor. That said, if the data is smaller due to compression, the time to write (or read) it to and from the disk might be a little less. Will it be enough to notice a change for the user? In a large implementation it might save some space on disk. I plan to give it a try. I just wish it had been released a couple months earlier because I just finished bringing a new server online and the initial data load is already done.
Yes I agree here.
We shouldn't forget that in the age of LZ4 people where already rocking the same amount of HDD"s, with comparable amounts of total throughput, on much less powerfull CPU's. It would scale quite nicely into the future, just like lz4 did! :)


We made 2 changes.
1 updated to U1 and used the new compression. our performance is actually not as good. so i'm still evaluating.
Can you print out the CLI specs of your dataset and post it here?


I'd did not have difference with lz4 vs zstd7 which is strange. Even more so the data wasn't compressed with zstd7 at all..
ZSTD 7 is quite a bit higher than LZ4 in compression levels!
Mind to post a readout of you dataset specs?
You did try writhing new data write? Changing the compression level does NOT change data already writen to disk!

Wanted to try it out to see for myself on a test system.
Performance with both was equal. Pool usage with zstd higher plus UI showed a ration of 1.0...
Any ideas?
Ratio of 1.0 means "compression off"

Want to replace the max gzip pools with zstd to gain a bit more speed on the archives..
With higher levels of ZSTD you would even see an actual improvement on compression levels in a lot of cases :)
You don't need ZSTD-7 though, the performance decrease is much higher than the ratio increase per ZSTD level. I would suggest ZSTD-5, it's almost as good (and an improvement in both ratio and performance over GZIP) as ZSTD-7 but quite a bit faster


Ok, I was curious and created a 2nd pool with zstd (default level, 3) and replicated the pool. Space savings are 5.7% compared to LZ4. As I haven't used the 2nd pool, I cannot tell anything about the performance, though.
5.7% sounds like your data isn't highly compressable or your recordsize is low...


Something I'm trying to wrap my head around is if you change the compression option for a dataset that already has many files inside, do the existing blocks get re-written eventually (under-the-mood maintenance) with the new compression method?
No, they are not.

What if you modify an existing file? Does the copy-on-write write the new blocks with the updated compression method, or with the file's / block's original compression method?
They get rewriten with ZSTD :)
you can also send-recieve locally to force all data to be rewriten with ZSTD ;-)
 
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They get rewriten with ZSTD :)
you can also send-recieve locally to force all data to be rewriten with ZSTD ;-)

The latter option (and the cleanest it seems) would require a lot of free space. At least it's something.
 

ornias

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The latter option (and the cleanest it seems) would require a lot of free space. At least it's something.
I combined it myself with spillitting big datasets into smaller ones, that way I could mv it in smaller pieces and send-recieve the bigger remaining datasets when that was done. Because it doesn't have to be one transaction ;-)
 

Herr_Merlin

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Doesn't matter which ZSTD level I seleced compression always stays at 1.0...
ofc copying data again to the test share after selecting another level of the algorhytem.
lz4 and gzip work fine.
 

ornias

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Doesn't matter which ZSTD level I seleced compression always stays at 1.0...
ofc copying data again to the test share after selecting another level of the algorhytem.
lz4 and gzip work fine.
Could you open a topic and add a "zfs get all tank/home" Readout
where tank/home is your zstd dataset?
I'll take a look tomorrow :)
 
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