Using Intel Cache Acceleration Software, what happens when a device is removed from a system when there is data in the Cache module?

[Stancey]

This could be considered "Floater" data which resides in Cash with no rotating storage to be written to for the purpose of purging it from cache. When the disk is reinserted, what is the state of the data that was cached? Presuming the rotating storage was NOT reformatted is the data rewritten to the drive even though the drive may have been invalidated?

[JosafathB_Intel]

Hello Stancey,

Thank you for contacting Intel® Memory & Storage Support.

We are going to be working on reviewing your inquiry related to the Intel® Cache Acceleration Software. We will be contacting you back as soon as we have an update or in case further information is required.

Thank you for your patience and understanding.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

[JosafathB_Intel]

Hello Stancey,

Thank you for your patience.

To answer your consultation, please review the information below:

Assuming "rotating storage" means a hard drive ( i.e. the Core device) if the Cache device gets removed from a system and if the Cache device had data that has not been flushed to the Core device:

The application will have to ensure it does not write to the Core or Cache device or attempt to read data that is only in the unavailable Cache device.

The data in the Cache device will be available once the Cache device is reinserted at which point data can be flushed once CAS (Intel® Cache Acceleration Software) becomes available again.

Even in case, the back end device/core device is an SSD instead of hard drive, the CAS software behavior is the same as mentioned above.

To further assist you, please provide us with the following information:

1. We will like to know the version/release of CAS you are using.
2. Are you using Open CAS or are you using the licensed version of our software?

We will be looking forward to your reply.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

[Stancey]

No, Josh You have it twisted around. The “Core device” as you call it or as old timers call it Rusty or rotating mass storage was removed and brought back into the system later. The problem is that the Cache Device retains information that has no backing store to push the data out to should it’s cache fill up. That presents a problem. My background is having worked on a Sperry Univac product called CADIS in the 1980s that handled such situations. I see no indication that there was any time designing around such situations. When I ran into the loss of a drive it became painfully apparent.

[JosafathB_Intel]

Hello Stancey,

Thank you for your reply.

Let us further investigate your comment “The problem is that the Cache Device retains information that has no backing store to push the data out to should its cache fill up. That presents a problem.” to provide you with more information.

To further assist you, please provide us with the following information:

1. We will like to know the version/release of CAS you are using.
2. Are you using Open CAS or are you using the licensed version of our software?

We will be looking forward to your reply.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

[Stancey]

We are using 3.2.2.64 Trial License version acquired by TEDL@geospan.com<mailto:TEDL@geospan.com>. I didn’t know there was an OPEN CAS product

[JosafathB_Intel]

Hello Stancey,

Thank you for your reply.

We are still investigating your inquiry “The problem is that the Cache Device retains information that has no backing store to push the data out to should its cache fill up. That presents a problem.” to provide you with more information.

We will be contacting you back as soon as we have an update or in case further information is required.

Thank you for your patience and understanding.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

[Stancey]

It is you who should be thanked by me for your patience with mw. I would be more than happy to provide more input should you need it but it is my understanding that you have access to the old Sperry and Unisys patents on the topic, though they don’t convey the experience of actually having worked with the older devices. I am still looking for info on the Open Cache product but have been pretty busy

[JosafathB_Intel]

Hello Stancey,

Thank you for your reply.

Let me add the following information to my previous post to try to clarify a little more the way that CAS works:

The application will have to ensure it does not read or write to the CAS device when the Core device (or Cache device) is removed. If a Core or Cache device is removed, we shouldn't write/read until the device is back. If a single point of failure is not ideal, customers can use a RAID solution such as VROC to mitigate such scenarios.

Also please review the following information about Open CAS:

Intel CAS for Linux has been moved to an Open Source project known as Open CAS. Functionally, Open CAS has the same features and capabilities as Intel CAS but is distributed and implemented in a slightly different way. Since the Enterprise version of Intel CAS for Linux is no longer available, we recommend you continue testing with Open CAS, which can then be used for the long term with no license fee. A quick start guide to get going with Open CAS can be found here:

https://open-cas.github.io/getting_started_open_cas_linux.html

As usual, it is a pleasure to assist you and if there is anything else that we can help you with, please do not hesitate to contact us back.

Have a nice day.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

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[Stancey]

Wait a minute, that is not possible. The CAS device is inserted transparently into the data stream without the application knowing the device is there. That is fundamental to ANY cache design. Thus the Applications running have no active knowledge the capability is even there. Again, I remind you that I worked with Cache systems as far back as the 70s and In the field and Engineering with products from 3 different manufacturers. Because of the integration with the operating system, the old Sperry CADIS package was far superior tp the competitors and the Sperry/Unisys XPC storage was based on the capability and knowledge base derive from CADIS systems. OS integration is key to preserving file system integrity. Thank you for the info on OpenCAS

[JosafathB_Intel]

Hello Stancey,

Thank you for your reply.

We are going to be working on investigating your inquiry to provide you with more information.

We will be contacting you back as soon as we have an update or in case further information is required.

Thank you for your patience and understanding.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

[JosafathB_Intel · Accepted solution]

Hello Stancey,

Thank you for your patience.

Based on the CAS Admin Guide (https://www.intel.com/content/www/us/en/support/articles/000006420.html) section 5.7, it says the following:

CAS will return an error to the application and stop processing IO when:

Data is being read from the cache but the cache device has failed and the data is not on the core device (dirty cache data)

Data is being written to the cache but the cache device has failed and the cache mode is write-back or write-only

Intel CAS will return an error to the application and continue processing IO when:

Data is being read from the core device but the core device returns an error

Data is being written to the core device but the core device returns an error

The application needs to handle the errors being returned accordingly. If the above behavior is not desired, consider using a RAID solution like VROC to mitigate single drive failures.

We hope you find this information useful.

Have a nice day.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

[JosafathB_Intel]

Hello Stancey,

We were reviewing your community post and we would like to know if you need further assistance with your Intel® Cache Acceleration Software or if we can close this community thread.

We will be looking forward to your reply.

Best regards,

Josh B.

Intel Customer Support Technician

A Contingent Worker at Intel

[Stancey]

As you wish