ramdisks [a solution]
Bill Davidsen
davidsen at tmr.com
Fri Apr 17 20:30:50 UTC 2009
Mike Wright wrote:
> Bill Davidsen wrote:
>> Mike Wright wrote:
>>> I came up with a solution that uses LVM and it works a *charm*,
>>> albeit, probably because of large block sizes relative to the 16M
>>> size of the ramdisks, seems inefficient (costs 25% each). Maybe I
>>> can tune these and get better.
>>>
>>> pvcreate /dev/ram15
>>> pvcreate /dev/ram14
>>> pvcreate /dev/ram13
>>> pvcreate /dev/ram12
>>>
>>> vgcreate my36Mdisk /dev/ram15 /dev/ram14 /dev/ram13
>>> vgcreate my12Mdisk /dev/ram/12
>>>
>>> lvcreate -n myRamDisk1 -L 36M my36Mdisk
>>> lvcreate -n myRamDisk2 -L 12M my12Mdisk
>>>
>> Wow that sounds complex, why not just make the ramdisks larger? Just
>> use the boot parameter which sets that:
>> ramdisk_size=N
>> where N is the size in kilobytes, so for 256M you specify 262144.
>>
>
> Thanks for that advice.
>
> I ended up making the ramdisks smaller which gave me greater
> granularity. Then when the volume groups were created I specified 64K
> extents instead of the default 16M. That gave two benefits: there was
> almost no wasted space in the VG, and the data that I copied over used
> less than half of the space of the original.
>
In thinking about this related to another issue, I remember that you can also
just create a single arbitrary ramdisk and mount it:
mount -t tmpfs -o size=270m tmpfs /mnt/tmp
which gives you a 270MB ramdisk on /mnt/tmp. No choice of filesystem type,
always tmpfs, but for what I wanted adequate.
I'm doing some testing on performance tips, and am using this for testing.
--
Bill Davidsen <davidsen at tmr.com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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