disk cache

ambad4u · Posted: Mon Jul 27, 2015 8:26 pm Post subject: disk cache

greetings to all,

some question(s):
I assume that TMPFS is for lightning fast read/write RAM based disk access.

is there similar to this just for disk cache? like utilizing normal sata drives and have RAM cache so that subsequent reads are very fast?

or is there anyone here used something like: "RapidCache" or something similar?

I'm still reading RapidCache for this, just would like to hear from a fellow gentoo if what they use as a disk cache.

I'll appreciate any inputs, thanks

eccerr0r · Posted: Mon Jul 27, 2015 9:26 pm Post subject:

Not sure I understand, free memory is automatically used as disk cache in Linux - up to all unused RAM... Then when there are program brk(), the cache is dropped for demand allocates.
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ambad4u · Posted: Mon Jul 27, 2015 10:17 pm Post subject:

i see, so linux does natively do disk cache if it permits..., I'll try to dig further on that.

anyways, I was referring to this website: http://rapiddisk.org/index.php?title=Main_Page

according to the website, it will utilize RAM as disk cache so that read is done in memory (RAM) and so will give significant I/O and speed in reading files.

Buffoon · Veteran Joined: 17 Jun 2015 Posts: 1369 Location: EU or US

http://www.linuxatemyram.com/

eccerr0r · Posted: Mon Jul 27, 2015 10:48 pm Post subject:

Not sure what rapiddisk is doing differently than what in kernel caching is doing, unless it is automatically detecting which files/blocks should be kept in RAM from fresh boot. Now that is a bit different behavior than stock.

The main trouble with in-kernel caching is that the cache is empty on cold boot - it has no idea what the hot pages were on the previous boot. Also though it handles writeback, it favors safety and will try to flush all buffers as soon as possible (if you didn't lengthen writeback time) and when writeback must occur, interactive performance suffers greatly.

Anyway it's good enough for me...
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Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?

Buffoon · Veteran Joined: 17 Jun 2015 Posts: 1369 Location: EU or US

You can use preload, but it can waste memory.

http://askubuntu.com/questions/110335/drawbacks-of-using-preload-why-isnt-it-included-by-default

ambad4u · Posted: Mon Jul 27, 2015 11:47 pm Post subject:

thanks for the inputs.

what I have is a regular sata drive that is regularly accessed by remote computers, I want it to cache what it has read. something that dm-cache, flashcache, bcache, RapidCache does.

I need something that I can manually allocate RAM and attached it as a read cache on a slow disk to improve speed and I/O access.

ambad4u · Posted: Tue Jul 28, 2015 2:43 am Post subject:

just read preload..., but is out of the question ^_^

RapidDisk is similar to TMPFS..., all I need is the other one which is RapidCache.
I'll try RapidDisk/RapidCache (if I can) and report back, thanks to all feedbacks/inputs