L2 SSD Raid-0 Cache

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bkostas
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L2 SSD Raid-0 Cache

Post by bkostas »

We currently use the following server for file sharing on an internet cafe business.

CPU: i3 6100
Motherboard: Z170
Ram: 16GB 3200MHz (usually no more than 4GB is used)
M2 SSD: 128GB Intel Pro 6000p for Windows 2008 Server
On-board Raid 10 (4x4TB HGST 7200rpm drives) - 8TB Total Storage
3x Intel 1Gbps Lan Cards in Team Mode

In total 25 Client PCs read from this server. They copy the requested application locally from the server and use individual performance to run it.
So what we need is to boost read speed across lan from server.

My thoughts are:
Use 8GB L1 Cache for C: as read only.
Use 2x 128GB Plextor M5Pro in software Raid-0 mode for L2 Cache as read only
Also the block of RAid10 is 4k. I was thinking of using 16k or 32k for L2 cache.

What do you think? Is that ok or do I need bigger SSDs?

Plan B is:
Don'y use L1 cache and let ram free in order to use 4k block on L2 cache.

thanks in advance!
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Re: L2 SSD Raid-0 Cache

Post by Support »

bkostas wrote:
Mon Mar 02, 2020 2:51 pm
Is that ok or do I need bigger SSDs?
It depends on how much hot-data is requested by the client PCs. Generally speaking, bigger cache space, better cache performance. As you might have known, the cache works by storing the data that were read and providing them on next read requests. If the amount of hot-data is big while the cache space is small, old saved cache contents might be replaced very often, causing bad cache effects and efficiency. Of course, if your hot-data is not much, you may not need to use big cache space otherwise it might be a waste of your investment.
bkostas wrote:
Mon Mar 02, 2020 2:51 pm
Plan B is:
Don'y use L1 cache and let ram free in order to use 4k block on L2 cache.
I prefer to use L1 cache.
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bkostas
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Re: L2 SSD Raid-0 Cache

Post by bkostas »

Hot data is around 200-250 GB (League of Legends / Fortnite / CSGO / PUBG - APEX)
So what do you recommend?
Use 8GB L1 Cache for C: as read only ?
Use 2x 128GB Plextor M5Pro in software Raid-0 mode for L2 Cache as read only or read/write?
What block size? Considering that RAid-0 has 4k.

thanks again.
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Re: L2 SSD Raid-0 Cache

Post by Support »

I prefer 8GB L1 + 2x128GB L2. Regarding the block size, when it matches the volume filesystem cluster size, the performance will be best. However, smaller block size might consume more additional overhead memory. If you see lots of memory overhead, you may increase block size.
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bkostas
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Re: L2 SSD Raid-0 Cache

Post by bkostas »

Do you suggest to use 8GB L1 + 2x128GB L2, both on drive D:? If yes then shall I create two tasks or one?
Also you didn't answer if you suggest me to use read only L2 or read/write? I don't have ups on server.

Many thanks
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Re: L2 SSD Raid-0 Cache

Post by Support »

Here are my thought for your reference: two cache tasks. One is for C: drive (I assume this is Windows partition) with 4GB L1 read-only. The other is for D: drive (I assume it's the 8TB storage) with 4GB L1 + 256GB L2, read only. You may use such configuration as a start and then tune the settings based on the real effect.
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bkostas
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Re: L2 SSD Raid-0 Cache

Post by bkostas »

Nice. Many thanks. I configured it as you suggested and I already see speed benefit.
But I have some questions.
When I try to create L2 cache for drive D: using Windows Raid-0 on 2x128GB SSD, it doesn't give me the option for 4K block. Only 8k and up.
For 8K the overhead is 5,52GB.
I added addition 2x16GB ram today in order to benefit more.
How should I use it?
I made L1 Cache task for C: with 4GB L1 read-only. Then another task for D: (8TB) with 8GB L1 + 256GB L2, read only, 8k block (5,52GB overhead).
Now I see ram usage at 22-24GB while I have 32GB.
How would you configure my setup?
Do you think it is worth using 32GB or just turn back to 16GB ?

Many thanks again. Great software.
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Re: L2 SSD Raid-0 Cache

Post by Support »

Because target volumes are too big, 4KB cache block size is not available. I would suggest 64KB (+) block size to reduce memory overhead.
bkostas wrote:
Wed Mar 04, 2020 8:50 am
Do you think it is worth using 32GB or just turn back to 16GB ?
If you have spare memory sticks, it's good to use 32GB RAM because bigger cache is always better. If it's a new investment, I'm not sure if it is worth or not. I think most performance boost is gained from the L2 cache. If you concern the speed more than the cost, well, add more RAM. Otherwise, I think 16GB is also workable.
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bkostas
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Re: L2 SSD Raid-0 Cache

Post by bkostas »

Ok. Nice. So far so good.
I have another question. What do you think is a good investment for me.
1. 1x 1TB NVMe and replace 2x128GB SSD
2. 64GB RAM for L1 cache
or
3. New Raid controller and combine with 2x128GB SSD L2 Cache

Also what do you think is the ultimate block size for my Raid10 ?

Finally, do you think I should Span or Stripe 2x128GB SSD ?
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Re: L2 SSD Raid-0 Cache

Post by Support »

bkostas wrote:
Wed Mar 04, 2020 7:07 pm
I have another question. What do you think is a good investment for me.
1. 1x 1TB NVMe and replace 2x128GB SSD
2. 64GB RAM for L1 cache
or
3. New Raid controller and combine with 2x128GB SSD L2 Cache
Well, as I said before, larger cache size, better performance. If you have enough budget, I think the first priority is 1TB NVMe SSD, then 64GB RAM.
bkostas wrote:
Wed Mar 04, 2020 7:07 pm
do you think I should Span or Stripe 2x128GB SSD ?
Stripe type has faster access speed, though a failure of either drive in a stripped volume will result in a total loss. Because you use it as read cache, so I think stripe would be better.
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