option to reallocate the cache overhead to SSD

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minhgi
Posts: 186
Joined: Tue May 17, 2011 3:52 pm

option to reallocate the cache overhead to SSD

Post by minhgi »

Hi SUpport,

Will there a plan to give user advance option to relocate the overhead memory to some other place like SSD? I think newer SSD these days should be fast enough to handle the overhead constant changes to track cached data. For a little performance loss, this would give the back the extra memory, especially on restrict laptop, to reallocate memory for a larger L1, 4K sector, or just for Windows. There any consideration for this option in the future?

Thanks,

minhgi

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Jaga
Posts: 484
Joined: Sat Jan 25, 2014 1:11 am

Re: option to reallocate the cache overhead to SSD

Post by Jaga »

Change what would normally be a few nanosecond operation to be more like 20-30 miliseconds? Sounds like a change that would slow everything down.

Pro-tip: don't use 4k cache sectors. I found the best for reading/writing is 64k on my machine. Even if you use 16k the overhead in Primo isn't bad on a smaller cache (which you would have on a RAM-limited laptop). 4k was never very useful in my opinion - larger means you take advantage of pseudo-read-ahead on defragmented spindle drives (exactly what you'd use on an older laptop).

minhgi
Posts: 186
Joined: Tue May 17, 2011 3:52 pm

Re: option to reallocate the cache overhead to SSD

Post by minhgi »

Yeah. So I set sector to 4K for a week and 16K another week, it seem the 16kb is over all faster due to the pseudo-read-ahead. It just I lost cache space in the L1\L2 cache. Oh well, you can't have a full cake but just a slice. It fine for now. Maybe another year downline, my request may get fulfil. Thanks for the suggestion, Jaga.

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support
Posts: 2709
Joined: Sun Dec 21, 2008 2:42 am

Re: option to reallocate the cache overhead to SSD

Post by support »

As Jaga said, this will affect the speed a lot, so we don't have plans to support this. However, we'll continue studying to reduce overhead.
Primo Ramdisk | PrimoCache
Romex Software Support

SolarDaveGreen
Posts: 3
Joined: Fri May 18, 2018 6:40 am

Re: option to reallocate the cache overhead to SSD

Post by SolarDaveGreen »

I have a 10GB L2 SSD cache (approximately) and 16k cluster size and the overhead is 800 bytes per cached cluster (just over 500 MB overhead), which seems like a lot of metadata to track a cluster in a cache.

I know it's hard work to make code more efficient. I appreciate your hard word and I like this software (I paid).

Can the 800 bytes per cluster overhead be reduced to 400 with clever coding, or more tightly packed structure, or ???

Thanks for listening.

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support
Posts: 2709
Joined: Sun Dec 21, 2008 2:42 am

Re: option to reallocate the cache overhead to SSD

Post by support »

V3.x already reduced the overhead amount a lot compared v2.x, making structure tightly packed. Other possible ways to reduce overhead will cost performance speed, so we haven't adopted them yet.
Primo Ramdisk | PrimoCache
Romex Software Support

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