Hard Drive Memory Cache

[jlpoolen]

I have 12 Reolink cameras running at full resolution at ~30 frames per second and I'm adding more. I've been using the Western Digital Purple series hard drive and generally. See https://github.com/scottlamb/moonfire-nvr/wiki/Hardware-Recommendations#hard-drives

I have had some problem, but I suspect it is the USB hard drive array which is a here-tody-gone-tomorrow Amazon brand, but for the last several months it has behaved.

I'm looking at adding another Western Digital Purple and notice there are three options for memory cache. The size of the drive is affected by which amount of memory cache you select. For instance, the largest drive, 14TB, only comes with a 128 MB cache. If I specify 256 MB cache, then the 14TB drive is not available, the largest is 10TB, so there is a trade-off.

With the high number of cameras, I'm saving "main" plus "subs", I would imagine more cache is better in case there might be any delays in saving data to the drive; however, this is pure supposition and theory on my part. I therefore thought I would start a discussion on this topic since I cannot find it addressed elsewhere in this project's site.

I found a Reddit discussion, but didn't learn much from it.

Is there a way to monitor or review what the cache's status is? Given the amount of video feeds I am throwing at a single disk, it would be interesting to learn if the quantity of feeds, e.g. 24, causes a bottleneck warranting a larger cache.

[jlpoolen]

I contacted Western Digital. Here's the dialog:

1. I asked:

I use a WD Purple for saving video streams, currently about 24 streams for one drive. I'd like to know how I can monitor or obtain statistics on the usage of the disk's buffer, sometimes referred as the cache. I want to know this because I want to add another Purple to my system for additional cameras and there is a choice of what the disk's cache size is and that necessarily determines the choice of storage sizes. So I'd like to see how my current one is holding up with the 24 continuous streams and see if I should have 256 or is 128 MB cache sufficient.

2. Response:

Thank you for contacting Western Digital Customer Service and Support. My name is Dave S.

I understand your concern that you want to know the cache size of your current WD Purple drive please be assured that I am here to help you.

Please allow me to inform you that as per the serial number 5PG75GVF which you have provided, you are using a WD Purple drive and its model number WD121PURZ and your drive has cache memory of 256 MB.

For more information you may refer to the link mentioned below:

https://www.westerndigital.com/en-in/products/internal-drives/wd-purple-sata-hdd#WD10PURZ

If in case I have misunderstood your issue please reply to this email and we will be happy to assist you further.

I will be waiting for an update from your end.

Sincerely,
Dave S

My follow-up:

Thank you, Dave S.
What I want to know is: how can I monitor the cache memory while the drive is active? Or, is there some way of logging what the cache memory utilized for a period of time, e.g. 30 minutes, is? I want to know if the cache is being totally utilized during operation, or if it is hitting the maximum limit causing Input/output to be delayed.

John

Their 2nd response:

Hello John,

Thank you for your reply.

Please be informed that Westen Digital don't provide any tool to monitor the cache memory while the drive is active you could try to search and use any third party tools to monitor the cache memory while the drive is active.

Please do not hesitate to reach out to me with any updates or further questions. If you prefer, you may also connect with one of our support specialists via live chat or phone call by clicking on the following link. We are always available to help you in any way that we can.

Chat: https://support-en.wd.com/app/chat/chat_launch

Phone: https://support.wdc.com/contact_phone.aspx?lang=en

Sincerely,
Dave S