[Gluster-devel] Using RAM-disks as bricks

[Jiri Hoogeveen]

On May 14, 2013, at 2:12 PM, Jeff Darcy <jdarcy at redhat.com> wrote:

> On 05/14/2013 07:07 AM, Jiri Hoogeveen wrote:
>> I did not tried it. But it is possible.
>> Create a disk image in /dev/shm
>> 
>> dd if=/dev/urandom of=/dev/shm/disk.img bs=1M count=100
>> losetup /dev/shm/disk.img /dev/loop0
> 
> I set up bricks on ramdisks all of the time when I want to isolate
> network/CPU bottlenecks on systems where all of that would otherwise be
> hidden behind the slowness of disks.  A couple of tweaks to the above:
> 
> (1) It's a little quicker to use /dev/zero instead of /dev/urandom.
> It's a minimal calculation per byte, but all of those bytes add up.
True, I use this mostly for encrypted disks, that why I use /dev/urandom for almost everything :)


> 
> (2) You'll need to do a mkfs before mounting.  Make sure e.g. to set an
> inode size of 512 or greater (just as we also recommend for normal
> filesystems).
> 
> (3) You can skip losetup if you use "mount -o loop".
Also true, old habits.


> 
> If you're doing this for a high-performance scratch area, I also suggest
> setting up multiple bricks (so long as they're not so small that you run
> into ENOSPC when manipulating large files).  The loopback driver is
> sadly single-threaded per device (historical note: it used to have more
> internal parallelism but then regressed) so the throughput will be
> noticeably limited by the speed of memory copies on a single core.

Thanks for this information, did not know this limit.


> 
>> 
>> 
>> Now is /dev/loop0 your ram based disk :)
>> 
>> Grtz, Jiri
>> On May 14, 2013, at 1:00 PM, Isak Nuhić <isak.nuhic at xlab.si> wrote:
>> 
>>> Hi,
>>> 
>>> is it possible to use ram-disks as bricks for building volumes in GlusterFS? I found an answer that it is not possible because ram-disk doesn't support extended attributes. Is there any way around it? I am trying to make a distributed volume with two ram-disk partitions as bricks but it doesn't work.
>>> 
>>> Thank you all in advance.
>>> 
>>> Isak 
>>> 
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>> 
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> 
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