L2 cache advise needed (SSD)

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RAMbo
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L2 cache advise needed (SSD)

Post by RAMbo »

I'm planning to buy a SSD for L2 use only.

System disk - 1 TB Samsung 860 EVO (SATA 600)
Several HDD that are mainly used for storage.
64GB RAM of which I can dedicate up to 32GB to PrimoCache if needed

I might cache some HDDs but my main focus is on the System disk.

The System disk has to endure lots of small writes from Usenet and some torrenting.
Besides that I obviously have software installed on my System disk. Some of it has database like read activities.

I looking for advise on the following:
- Block size of the L2 SSD
- Specificics about ideal L1/L2 setup.
- Specs of the L2 SSD

The specs of the SSD are most important right now as that's the component I still have buy.
It likely will be a PCIe3x4 SSD.
But what should I focus on? Sequentional speed or random (IOPS) speed.
I know IOPS are important, but I must admit I don't know what the ideal balance between IOPS and sequential speed is.
Does the importance of IOPS get less when using L1 cache?

Or is it better to ditch the whole L2 cache idea and just use the money saved to buy a faster system SSD?
Perhaps another 1 TB Samsung 860 EVO (SATA 600) and stripe them?
(Yeah, I do many backups...)
But I have my reservation on RAID 0. Will it really perform good without a dedicated quality RAID card? Or will it just waste a lot of CPU cycles without decent speed benefit.


That's it. I asked my question. Obviously I would like them to be answered but I'm also open to any other relevant advise.
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Jaga
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Re: L2 cache advise needed (SSD)

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Normally you wouldn't use L2 caching (a SSD or NVME) on another SSD - it can kill performance due to unnecessary shuffling and operations.

Due to the amount of memory in the system, you should leave the L1 block size equal to the cluster size on the volume (usually 4k). It'll eat some RAM, but give the best performance.

I think IOPS for torrenting/usenet would be preferable over sequential, especially since SSDs and NVMEs aren't defragmented.

I haven't ever done software RAID 0 on a system volume, and don't think I'd recommend hardware RAID 0 on the Samsung drives (it disables all TRIM functionality). If you're looking for the best speed on the system drive, along with the best longevity against heavy writes, you'll probably want one of the Pro SSDs from Samsung, then use a good sized read/write L1 (if you have a UPS you can enable write caching in Primocache, further speeding up the system). Skip the L2 entirely.
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Re: L2 cache advise needed (SSD)

Post by Support »

Use a faster NVMe SSD as L2 cache can also speed up SATA SSDs. If you have spare money and would like to buy a NVMe SSD, I recommend that you reinstall Windows OS directly on your new fast SSD to get best performance.
If you want to save money and just keep current hardware configuration, you may use RAM (L1) cache for your SATA SSD. If your system partition doesn't contain any personal data and well backup-ed, you may enable PrimoCache Defer-Write which will increase writing performance a lot and reduce writes to your SSD.
For your reference, here is my workstation setting. I partitioned my SSD into 2 drives, one for Windows OS and programs, and the other for my data. I regularly backed up Windows partition, so I can safely use Defer-Write on the Windows partition and get a good read and write performance.
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Jaga
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Re: L2 cache advise needed (SSD)

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support wrote: Tue Dec 11, 2018 3:08 am Use a faster NVMe SSD as L2 cache can also speed up SATA SSDs.
That's interesting - I figured the overhead for doing NVME L2 operations would have killed the overall IOPS speeds.
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RAMbo
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Re: L2 cache advise needed (SSD)

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Jaga wrote: Tue Dec 11, 2018 6:19 am
support wrote: Tue Dec 11, 2018 3:08 am Use a faster NVMe SSD as L2 cache can also speed up SATA SSDs.
That's interesting - I figured the overhead for doing NVME L2 operations would have killed the overall IOPS speeds.
Maybe it kills the IOPS the moment it's cached on the L2-NVMe. But after that benefitting starts.
So I think it greatly matters how efficient the caching prediction is. How often does the cache gets flushed out by say copying a 50GB file.
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RAMbo
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Re: L2 cache advise needed (SSD)

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Jaga wrote: Mon Dec 10, 2018 10:20 pm If you're looking for the best speed on the system drive, along with the best longevity against heavy writes, you'll probably want one of the Pro SSDs from Samsung, then use a good sized read/write L1 (if you have a UPS you can enable write caching in Primocache, further speeding up the system). Skip the L2 entirely.
I'm still considering what's best.

Longevity sounds good but comes at a cost. I'm wondering it's worth the premium. Lemme explain.
The pro series cost more and give you more writes. That sounds good.
The other side of the coin is that SSDs are evolving fast.
Perhaps a it's a better option to use up a SSD in a 'short' time and then just buy what's new right then. Likely much faster and bigger for the same price.
The premium for the pro version could go to the next drive.

In syntetic benchmarks the bleeding fast SSD are just that, bleeding fast. That's just a fact.
But when more real life benchmarks are run like game, PCmark, etc, the difference gets a lot less.
My guess is that putting PrimoCache on top of it, makes the difference even less.
Simply because PrimoCache's ultimate goal is to stop all disk access and run everything from cached memory. Obviously that's never going to happen but that's the aim. My point is floppy, cd, HDD, SSD all seem to have the same speed when things run from PrimoCache cache.
In other words PrimoCache closes part of the gap between a quite good SATA600-SSD and a NVMe-SSD speedwise. An important side effect is that the writes are vastly reduced and with that the need to go Pro for that extra TBW might be no longer valid (for everyone)

I have no UPS*, but will use deferred write anyway. I backup very frequently. The stuff I'm actually working on gets backed up every hour. That will cut down writes even more.

*=Where I live powercuts are extremely rare.


But....
While I'm quite sure the above is true, I don't have numbers on how efficient PrimoCache handles it.
I mentioned two big disk trashers: Usenet and torrents.
IF PrimoCache is able to cache those tiny blocks that only exist for a few seconds the above story is very valid.
IF PrimoCache fails to chache those blocks, then the above story is far less valid because the SSD will still be worn down at top speed.
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RAMbo
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Re: L2 cache advise needed (SSD)

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support wrote: Tue Dec 11, 2018 3:08 am Use a faster NVMe SSD as L2 cache can also speed up SATA SSDs. If you have spare money and would like to buy a NVMe SSD, I recommend that you reinstall Windows OS directly on your new fast SSD to get best performance.
When I buy a NMVe it will be one of the faster ones. They start at around 1500MB/s, but I want something of above 3000MB/s.
That automatically means it will be a >480GB SSD.

And that comes pretty close to what I need as a system disk. Especially if I don't just dump everything on it as I do now.
The NMVe serves as a system disc with PrimoCache to speed up things a bit more.
My current SATA-600 SSD could serve as download disk. I only have 50Mbyte/s down so that's fast enough. I'll put PrimoCache on it to reduce disc access.

I need some advise on how to setup that SATA SSD.

I could just dedicate 20GB cache to it, but that's not a very professional way to handle it.
For usenet I use NewsLeecher which downloads 1000s of articles of a few hundred KBytes and glues them together into larger .rar files of usually 50-100MB. Those files are unpacked and can result in a large 20GB file or a bunch of files of all sizes.
What is the best approach for that situation?
I do want to cache the small articles because they only exist for a short while.
I do not want to cache the larger files because they mainly are a 1x write and 1x read and then get deleted.
How can I keep the cache small but useful for those small files, without the large files flushing the cache?
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Re: L2 cache advise needed (SSD)

Post by Support »

RAMbo wrote: Tue Dec 11, 2018 11:21 am For usenet I use NewsLeecher which downloads 1000s of articles of a few hundred KBytes and glues them together into larger .rar files of usually 50-100MB. Those files are unpacked and can result in a large 20GB file or a bunch of files of all sizes.
What is the best approach for that situation?
I do want to cache the small articles because they only exist for a short while.
I do not want to cache the larger files because they mainly are a 1x write and 1x read and then get deleted.
How can I keep the cache small but useful for those small files, without the large files flushing the cache?
Is it possible you generate large files to another partition without cache? You may just cache the partition in which downloaded files are stored.
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Jaga
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Re: L2 cache advise needed (SSD)

Post by Jaga »

support wrote: Thu Dec 13, 2018 3:00 amIs it possible you generate large files to another partition without cache? You may just cache the partition in which downloaded files are stored.
That's essentially what I do with multi-part FTP downloads - the temp folder for the .parts is on a separate un-cached drive.
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