Hello.
I have a RAID 0 consisting of 4 drives as a scratch disk.
Sequential performance is good, but I would like to add ssd cache to improve oddball/random R/W performance.
For an average 30 or 60GB ssd as the cache, what can I expect ?
what can i expect from raid 0 + cache ssd?
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BonzaiDuck
- Level 7
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- Joined: Wed Jan 11, 2017 12:57 am
Re: what can i expect from raid 0 + cache ssd?
You can expect something like 80% of the spec performance of the caching device.
We had a recent discussion of this over at AnandTech forums' "Memory and Storage". It is easy to reach the erroneous conclusion that the cached speed performance will be significantly influenced by the speed of the source drive configuration. Maybe only a little, because -- again -- the limiting factor is the speed of the caching device.
I guess what I'm saying is that you choose to RAID 0 your SSDs, and that's "already done." You might ask "what's the sequential throughput benchmark for the RAID array?" I'm assuming you are using HDDs -- electromechanical hard disks. I remember when I had 4x SATA HDDs in RAID 5, but my scores were limited to maybe 400 MB/s. This had been influenced as well by the PCIE version of the motherboard.
If you use an NVME M.2 drive as the caching volume, you might see sequential read rates of possibly 2,000 MB/s. (The Samsung 960 Pro/EVO specs are around 3,000 to 3,500). That could be likely whether you're caching a source configuration of a single HDD, RAID0 or RAID5.
However! To cut to the chase! The 4K Random read specs on even the Samsung NVME's doesn't prove too well. If you can configure a 3dXPoint NVME device as cache, they would be significantly better than that.
And -- However again . . . If you instead cache to a sufficient quantity of RAM, then you'll see the 4K random bench results possibly as high as 900 MB/s. You can also have a two-tiered cache -- a combination of RAM-caching and SSD-caching on the same source configuration (your RAID array, for instance.) What's your native 4K random read performance on the RAID0?
We had a recent discussion of this over at AnandTech forums' "Memory and Storage". It is easy to reach the erroneous conclusion that the cached speed performance will be significantly influenced by the speed of the source drive configuration. Maybe only a little, because -- again -- the limiting factor is the speed of the caching device.
I guess what I'm saying is that you choose to RAID 0 your SSDs, and that's "already done." You might ask "what's the sequential throughput benchmark for the RAID array?" I'm assuming you are using HDDs -- electromechanical hard disks. I remember when I had 4x SATA HDDs in RAID 5, but my scores were limited to maybe 400 MB/s. This had been influenced as well by the PCIE version of the motherboard.
If you use an NVME M.2 drive as the caching volume, you might see sequential read rates of possibly 2,000 MB/s. (The Samsung 960 Pro/EVO specs are around 3,000 to 3,500). That could be likely whether you're caching a source configuration of a single HDD, RAID0 or RAID5.
However! To cut to the chase! The 4K Random read specs on even the Samsung NVME's doesn't prove too well. If you can configure a 3dXPoint NVME device as cache, they would be significantly better than that.
And -- However again . . . If you instead cache to a sufficient quantity of RAM, then you'll see the 4K random bench results possibly as high as 900 MB/s. You can also have a two-tiered cache -- a combination of RAM-caching and SSD-caching on the same source configuration (your RAID array, for instance.) What's your native 4K random read performance on the RAID0?
Re: what can i expect from raid 0 + cache ssd?
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CrystalDiskMark 6.0.0 x64 (C) 2007-2017 hiyohiyo
Crystal Dew World : https://crystalmark.info/
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* MB/s = 1,000,000 bytes/s [SATA/600 = 600,000,000 bytes/s]
* KB = 1000 bytes, KiB = 1024 bytes
Sequential Read (Q= 32,T= 1) : 602.250 MB/s
Sequential Write (Q= 32,T= 1) : 435.854 MB/s
Random Read 4KiB (Q= 8,T= 8) : 5.009 MB/s [ 1222.9 IOPS]
Random Write 4KiB (Q= 8,T= 8) : 3.426 MB/s [ 836.4 IOPS]
Random Read 4KiB (Q= 32,T= 1) : 4.661 MB/s [ 1137.9 IOPS]
Random Write 4KiB (Q= 32,T= 1) : 3.381 MB/s [ 825.4 IOPS]
Random Read 4KiB (Q= 1,T= 1) : 1.401 MB/s [ 342.0 IOPS]
Random Write 4KiB (Q= 1,T= 1) : 3.678 MB/s [ 897.9 IOPS]
Test : 1024 MiB [G: 0.1% (2.8/2047.8 GiB)] (x5) [Interval=5 sec]
Date : 2018/03/16 0:57:33
OS : Windows 10 Professional [10.0 Build 16299] (x64)
Re: what can i expect from raid 0 + cache ssd?
Not interested in RAM cache just yet because of how crazy expensive fast DDR4 modules are.
Re: what can i expect from raid 0 + cache ssd?
No need really for super fast RAM modules. Even average RAM for L1 makes L2 on a SSD look silly by comparison.Hexile wrote:Not interested in RAM cache just yet because of how crazy expensive fast DDR4 modules are.
Re: what can i expect from raid 0 + cache ssd?
Certain workloads require at least 2933 MHz to have enough bandwidth in my case so that forces me to use expensive memory.Jaga wrote:No need really for super fast RAM modules. Even average RAM for L1 makes L2 on a SSD look silly by comparison.Hexile wrote:Not interested in RAM cache just yet because of how crazy expensive fast DDR4 modules are.
I have ran the numbers already and determined 3333MHz is the best option.