Fwd: Why rapiddisk cache, better then build-in ram cache?

[Timofey Titovets <nefelim4ag@gmail.com>]

Hello list,
I'm very sorry, what i've forward mail it to linux-mm list, but i
can't find any mailing list like linux-block-io or something like that
%)

I've recently find rapid cache and it confuse me, as i know, linux use
almost all free ram for IO caching and do it very cool and fast.
May be i misstake in something? May be linux memory io cache sub
system not fast as i think?

---------- Forwarded message ----------
From: Petros Koutoupis <pkoutoupis@inverness-data.com>
Date: 2015-06-11 18:33 GMT+03:00
Subject: Re: Why rapiddisk cache, better then build-in ram cache?
To: Timofey Titovets <nefelim4ag@gmail.com>
Копия: support@inverness-data.com


Timofey,

Thank you very much for you interest in the project.
Linux does not have a built block I/O cache. All block I/O resides in
a temporary buffer until the schedular schedules the task to the block
device; that is, unless you are running Direct I/O in which all I/O is
immediately dispatched regardless of the schedular. Now a file system
will cache data in the VFS layer but this cache is somewhat small and
limited. With RapidDisk / RapidCache, you can easily enable 1GB or
even 1TB of cache to a slower block device, thus enabling a block
based cache. Or you can simply just enable a large RAM based block
device and not use it as a cache. I guess it all depends on your
requirements.

You are correct, though. This should be detailed on the Wiki and I
will definitely address it. Thank you for bringing it to our
attention.

On Thu, Jun 11, 2015 at 10:26 AM, Timofey Titovets <nefelim4ag@gmail.com> wrote:
>
> Hello,
> i've read http://rapiddisk.org/index.php?title=Main_Page
> That a very cool,
> but i can't understand why it better than linux built in file/block io cache?
>
> May be you can explain it on wiki page?
>
> --
> Have a nice day,
> Timofey.

--
Petros Koutoupis
Inverness Storage Solutions, LLC
312-854-9707
pkoutoupis@inverness-data.com

-- 
Have a nice day,
Timofey.

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