L2 cache vs. Tiered Storage Spaces

[crawl]

Hello guys,

Tried to find the answer in forum, found several interesting cases and discussions about L2 cache and MS Storage Spaces,
but somehow nothing that would answer my question. Comments or recommendations needed.
Suggested environment (although it's not so important as question is more architectural):
Two identical nodes in hyper converged cluster running Windows Server 2016 Datacenter:
hardware RAID controller available
2 SSDs and 4 HDDs dedicated for storage (with capacity ratio SSD/HDD – 1:10)
one NIC with 2x10Gb and MB integrated - 4x1Gb
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1x10Gb – StarWind sync, directly connected;
1x10Gb – StarWind iSCSI targets, directly connected;
3x1Gb – Cluster live migration, directly connected;
1x1Gb – Management, plugged into switch.
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As I understand it’s advised to use hardware RAID10, if available, for the storage.
The question is which way would be more beneficial to use SSDs to improve HDDs’ performance:
1) Configure SSD RAID10 disk and HDD RAID10 disk using RAID controller and use SSD RAID10 disk as L2 cache for StarWind flat image disks;
2) Configure SSD RAID10 disk and HDD RAID10 disk using RAID controller, pool both disks to storage spaces, create simple tiered virtual disk
for StarWind flat images and let windows distribute the data between tiers depending on usage frequency and refuse using L2 cache.
First choice, I suggest, will improve reads, while second – reads and writes, but adding additional software layer will mean additional processing loads.
Also i didn't investigate on which level MS Storage Spaces work distributing data between tiers, so possibly, if it's not a block level and OS will see only
a single StarWind image file, it will be unable to use tiers?
I'm quite fresh as concerns storage matters, so sorry in advance if asking obvious or dumb things.

[PoSaP]

Hi crawl,
I read your post and have some suggestions about it.
In case if you use StarWind flat image disk with L2 cache, it will improve reads, because of cache in Write-Through mode by default. But for RAID 10 you need at least 4 disks, that is why in your configuration I think it will be RAID 1 for SSDs and RAID 10 for HDDs.
In case of storage spaces, SSDs will be used to improve reads and writes. From my experience, it will be very noticeable additional processing load. As far as I know, according to Microsoft recommendations, disks must be connected directly to Windows, not in the RAID array - and I am not sure you could do it in the way you wrote. Have you tried to play with it already?

[crawl]

Hi PoSaP,

many thanks for your input. You are absolutely right as concerns SSDs - a simple mirror was meant.
I didn't build a test lab yet, had an intention to hear some comments and suggestions before collecting the disks.
For the moment I only have two Intel blades R1304GZ4GC with dual Xeon E5-2630 v.2 2.6GHz and 64GB of RAM in each to play with.
This intended to spin some 6-8 VMs, but more or less heavy will be only two - Exchange 2016 with some 1TB of databases
and a SQL Server with 256GB database. Other VMs are 3 DCs and several Linux based, all with less than 64GB of disk space requirement.
Major requirement is prevention of any data loss especially as concerns SQL Server, availability is important but secondary.
In my opinion processing power for the planned tasks is quite excessive, so some part could be sacrificed for the Storage Spaces if needed.
In truth, my preference is L2 cache, as it's more simple solution, but management is obsessed with the Storage Spaces and tiering idea,
especially as it could give some kick to writes.

[Oleg(staff)]

Hi crawl,

Let me try to answer your questions.
StarWind works on Tiered Storage Spaces with pretty good results and we have hybrid Hyper-Converged Appliances based on Storage Spaces as underlying storage. Yet, I am afraid you have not enough SSD capacity to gain good results since Microsoft recommendation is to use 30% of SSD storage capacity inside the Tiered Storage. And, as Posap said there will be very noticeable additional processing load. Please, check this link:
https://blogs.technet.microsoft.com/lar ... r-2012-r2/
As for L2 cache usage, it is recommended for highly read-intensive environments where read operations take up to 80-90%.
Based on your explanations you can consider another option for storage configuration. For example, you can put critical, performance-hungry VMs on SSD RAID and all other VMs on HDD RAID. For RAID array creation recommendations check this link:
https://knowledgebase.starwindsoftware. ... ssd-disks/