ramdisks [a solution]

[Bill Davidsen]

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