Ron Johnson <[EMAIL PROTECTED]> wrote:
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> On Sunday 22 July 2001 16:32, Adrian wrote:
> > Hi,
> >
> > This is a fool question but I need some help:
> >
> > How build a ramdisk in LM 8? ...
> Surely, I won't be the only one to say this, but here goes:
> 1. Trust linux. It does a good job of caching data.
> 2. The more RAM that you use for a RAM disk, the less RAM that
> the PC will have for "regular" use, and so the more likely
> that it will have to use the swap files.
(Note that there was another answer talking about why ram disk
is faster than cache, I don't wish to go there right now, sorry.)
(I've been running something performance monitoring software which
is (sort of) from Sun (called SE Performance Toolkit - really
cool, even though it missed a thing or too), and it has been
instructive - I wish we had something like it for Linux! I've
learned a little more about performance enhancements through
watching what it detects...)
Ok, to the point:
1 - ram is fast, disk is slow. (For very LARGE values of slow!)
Before worrying about ramdisk, make CERTAIN that you have
plenty of RAM for cacehing to do its job. If you don't have
enough ram, adding a ramdisk will simply make programs start
running from the disk, which is worse than 'simply' having
data accesses hit the disk. If you can have enough ram
to hold the entire database AND the program AND the OS
AND anything else that needs to run, then you're starting
where you want ;-) and can THEN consider other issues.
2 - after writing all that, i went back and re-read your initial
query. What exactly is the test supposed to measure?
'copying a database to it' - are you trying to measure
the database access speed? Data transfer rates from the
database? Something else? Or are you doing what I assumed -
trying to make the database run faster? Depending
upon what you're trying to do will result in different
answers...
if you are just trying to measure transfer rate, send the
data to /dev/null - that's pretty fast ;-) (and does not
require memory :-) But beware - running the same command
twice in a row will most likely result in MUCH different
numbers, because of cacheing (assuming you are not memory
constrained). (I could tell a story here, but I won't ;-)
rc
(note - bcc copy sent to Adrian - hopefully the list won't see but one!
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