L2 Write-back cache

[RyanNW]

Hello,

Just noticed that the management console no longer provide ways for creating L2 write-back cache. Will the option appear again in future version?

Thanks
Ryan

[Michael (staff)]

Hello RyanNW,
Write-Back mode for L2 cache was turned off about year ago. It is planned to turn it on once experimental L2 cache will be approved to use in Production.

[RyanNW]

Hello Micheal,

Thanks for your update. I am testing the experimental L2 cache as well since I got some performance issues with the production L2 cache. BTW, it seems like editing the configuration file will turn the write-back mode back on for flat image file. Am I correct?

Anyway, looking forward for the production release of the experimental L2 cache.

Cheers,
Ryan

[Michael (staff)]

Ryan,
Yes, you are correct, it is possible, but it is NOT recommended.
Of course, we will keep the community updated.

[cjchilling]

In view of the discussion above:

Is there a paper with the current best practices regarding Cache allocation and settings?

Thanks

[Michael (staff)]

Hello cjchilling,
You can find StarWind Best Practices document with cache recommendation here:https://www.starwindsoftware.com/techni ... ctices.pdf
The cache settings are depending on total workload to the storage. The base recommendation is to put 1 GB of L1 cache in Write-Back mode per 1 TB storage capacity. L2 cache - 10% of the total capacity of the corresponding device.
Basically, configuring bigger cache size will give you better performance.

[mcamino]

I am curious what type of risks we would have with L2 write-back cache enabled? My understanding of the process is the data is written to the SSD L2 Cache and then flushed to the SATA/SAS Spinning disks. If the server lost power or hard rebooted that data would then be flushed upon reload from SSD to the Spinning disks. No Data Loss. The issue with L1 Write back cache is if the same server loses power or does a hard reboot , the memory is lost and the data corrupted. I am by no means an expert, i am just asking the question to help better understand the risks and performance gains of L2 caching. Today in our test lab we dont use SSD L2 Caching, but we are discussing the merits of LSI Cachecade vs Starwind L2 cache. I have read your other posting specifically on this topic, and how starwind has much better benefits then the LSI Cachecade. We are looking for a solution that will provide write-back caching in a SAFE manner.

[John (staff)]

Hello Mcamino

It was found if you run L2 write-back cache with writes workload yours SSDs will be getting huge amount of damage.

I am curious what type of risks we would have with L2 write-back cache enabled? My understanding of the process is the data is written to the SSD L2 Cache and then flushed to the SATA/SAS Spinning disks. If the server lost power or hard rebooted that data would then be flushed upon reload from SSD to the Spinning disks. No Data Loss. The issue with L1 Write back cache is if the same server loses power or does a hard reboot , the memory is lost and the data corrupted. I am by no means an expert, i am just asking the question to help better understand the risks and performance gains of L2 caching. Today in our test lab we dont use SSD L2 Caching, but we are discussing the merits of LSI Cachecade vs Starwind L2 cache. I have read your other posting specifically on this topic, and how starwind has much better benefits then the LSI Cachecade. We are looking for a solution that will provide write-back caching in a SAFE manner.

[kevrags]

Hello Mcamino

It was found if you run L2 write-back cache with writes workload yours SSDs will be getting huge amount of damage.

I am curious what type of risks we would have with L2 write-back cache enabled? My understanding of the process is the data is written to the SSD L2 Cache and then flushed to the SATA/SAS Spinning disks. If the server lost power or hard rebooted that data would then be flushed upon reload from SSD to the Spinning disks. No Data Loss. The issue with L1 Write back cache is if the same server loses power or does a hard reboot , the memory is lost and the data corrupted. I am by no means an expert, i am just asking the question to help better understand the risks and performance gains of L2 caching. Today in our test lab we dont use SSD L2 Caching, but we are discussing the merits of LSI Cachecade vs Starwind L2 cache. I have read your other posting specifically on this topic, and how starwind has much better benefits then the LSI Cachecade. We are looking for a solution that will provide write-back caching in a SAFE manner.

That's what the other vendors do, though. Have a hot SSD tier for reads and writes. I understand you need an SSD with enough write endurance, but seeing that we built an all-flash server for VDI using Starwind, this is supported, isn't it?

[Michael (staff)]

Currently, StarWind uses SSD as L2 cache in write-through mode - only for reads.
There are no issues with using SSDs as underlying storage for all-flash scenarios with StarWind - it works great!