Defining multiple 2nd level caches does not work Topic is solved

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Axel Mertes
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Defining multiple 2nd level caches does not work

Post by Axel Mertes »

Hi!

I've just tried to use FC for volumes. I have three volumes on that machine (C:, D; and SSD F:). The config was as follows:

C:
1st Level Cache: 1024 MB RAM, R/W, 4KB Blocks
2nd Level Cache: 8192 MB on SSD F:

D:
1st Level Cache: 2048 MB RAM, R/W, 4KB Blocks
2nd Level Cache: 16384 MB on SSD F:

I can clearly start and stop the two caches independently, but there is only one "fancycache.sys" file on the SSD.
Either the second one activated is not being created at all (when I first created C: with 8192 MB cache, the file was just that small) or it may try to use the cache file for BOTH volumes?
I would not want to give this a real shot, as this might result in total system corruption in worsed case.

However, it should be possible to use one SSD as host for multiple individual 2nd Level cache files. So my suggestion would be to give them individual names like "fancycache_c.sys" and "fancycache_d.sys" as example.

Regards,
Axel
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Re: Defining multiple 2nd level caches does not work

Post by Support »

Hi,

Current beta version doesn't support to use one SSD as host for multiple individual 2nd Level cache.
Axel Mertes
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Re: Defining multiple 2nd level caches does not work

Post by Axel Mertes »

Willt hat option become available in future?

It would be VERY helpful. So we could use a high quality SSD as entire "system cache", regardless of from where files are being read. The RAM could be used as the buffer for deferred writes to the 2nd level cache.

Btw, as you did already quite a bit on statistics.
I am not so much interested in statistics during runtime, but prior to installing such a tool and a caching SSD, and potentially additional RAM.

So I got the idea if it would be possible for you to make a simple tool that measures how much new blocks are read/written during a day, how often they have been overwritten with new data etc. to get a real idea how large an SSD cache should be to buffer say a full working day of transactions without ever running out of cache space.

Imagine, we are doing film postproduction here. We do over and over play the same image sequences from the server drives (or sometimes local drives). Then we render new image sequences iteratively, resulting in new modified data. It would be good to know how much data is really being touched during a day, and clearly if data gets read many times, it need to be counted only once in the statistics for "required cache size" but it should be counted each time in the statistics for "data transferred in total".

I think with such a tool one can easily identify the demands and bottlenecks and plan the right size for an SSD cache and RAM extension.

In a perfect world:

1. You could measure your required average "day by day" cache needs.
2. You install a SSD that is at least as large as the measured cache needs.
3. You have enough RAM to allow deferred writes caching from all you connected volumes, regardless if local or network shares.
4. You can activate FancyCache to do transparent caching of all you accessed data to a superfast local RAM 1st level and SSD 2nd level cache.

This strategy would make you local machine simply as fast as thinkable, and offload network traffic to the thinkable minimum.

Regards,
Axel
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Re: Defining multiple 2nd level caches does not work

Post by Support »

Axel Mertes wrote:Willt hat option become available in future?
Yes.

PS. currently statistics shows the free bytes of the level-1 and the level-2 cache, so you can measure how many cache needed.
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Re: Defining multiple 2nd level caches does not work

Post by Support »

implemented in version 0.6.0
Axel Mertes
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Re: Defining multiple 2nd level caches does not work

Post by Axel Mertes »

Great, I am testing this already. Thanks!

Axel
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