Re: [Lustre-discuss] Failover Setup MDS/MDT
Brian J. Murrell
>
> How can one determine the size for the MDT partition or is that the same as
> the MDS device ?
> (As far as i can see the MDT takes the DIR info etc. So it should be larger
> than the MDS.)
An MDT is the device (i.e. the disk) that Lustre in an MDS (the server)
uses to manage the metadata. Maybe that clears it up?
b.
Brian J. Murrell
>
> Well yes ok, but what about the sizes of the partitions ?
>
> The docs present an example calculating the inode space needed on an 'MDS'.
> (3.2.2 Calculating MDS Size)
That should technically be "MDT Size", not MDS size.
> So when the MDS partitions
AKA MDTs.
> holds the inodes of the lustre system what will be
> the partition size of the MDT device ?
You are talking about two things that are in fact one and the same. The
"MDS partition" is the MDT.
> Or should it read 'MDT' partition size in the docs and the MDS partition size
> doesn't matter at all ?
Indeed. Can you file a bugzilla ticket regarding that that bad use of
MDS? I will see that it gets to the documentation team.
Thanx,
b.
Sheila Barthel
Section 21.3.2 is Calculating MDT Size, which includes an inode
calculation example and does not refer to the MDS.
http://manual.lustre.org/manual/LustreManual16_HTML/LustreTuning.html#50446384_pgfId-1291157
Please clarify which Lustre manual version you are referring to.
Sheila
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Heiko Schroeter
> On Friday 20 June 2008 16:08:23 Brian J. Murrell wrote:
> > On Fri, 2008-06-20 at 16:01 +0200, Bernd Schubert wrote:
> > > We do it for several lustre installations and it works fine.
> >
> > Have you done any "intensive" failover testing of it? I'm thinking
> > something along the lines of our Hendrix/CMD test 11 or 17. In those
> > tests we had to survive a constant stream of failovers at something like
> > 3 or 5 minute intervals for 24 hours. So yes, a hundred or two
> > failovers in a row and no application (i.e. userspace) errors.
>
> I don't think we did these tests yet, but I could put it onto my TODO list,
> if you think it is important. So far drbd always perfectly did its job and
> never was an issue here (in contrary of the many many hardware problems we
> often have).
The failover takes about 3-4 minutes in our setup with an shared MDS and MDT
running a mirrored DRBD device.
As far as we can see it this is taken by the fsck on the DRBD device when
HEARBEAT takes over.
The MDS/MDT partition used in this test szenario is 20GB in size running in a
1.8GHz AMD machine.
Just one more question about the partition sizes. As the docs points out one
determines the size for the MDS partition by the number of inodes.
How can one determine the size for the MDT partition or is that the same as
the MDS device ?
(As far as i can see the MDT takes the DIR info etc. So it should be larger
than the MDS.)
Thanks
Heiko
Heiko Schroeter
Well yes ok, but what about the sizes of the partitions ?
The docs present an example calculating the inode space needed on an 'MDS'.
(3.2.2 Calculating MDS Size)
That what actually confuses me a bit.
So when the MDS partitions holds the inodes of the lustre system what will be
the partition size of the MDT device ?
Or should it read 'MDT' partition size in the docs and the MDS partition size
doesn't matter at all ?
Thanks and Regards
Klaus Steden
Hello Heiko,
If I'm not mistaken, 'MDS' refers to the metadata _server_, while 'MDT'
refers to the metadata _target_, i.e. the distinction is akin to that
between 'OSS' and 'OST'. The MDS is a server node; the MDT is the volume
where all the metadata for your volume is stored.
The handbook recommends an MDT size about 1-2% of the size of your total
volume size, i.e. if your total CFS volume is 10 TB, the MDT would be about
200 GB. This is fairly conservative, so you may want to err on the side of
growth by using a larger volume than that. If you can spare the disk, you're
certainly not sacrificing anything by over-provisioning your MDS.
hope this helps,
Klaus
On 6/25/08 5:29 AM, "Heiko Schroeter" <schr...@iup.physik.uni-bremen.de>did
etch on stone tablets:
Heiko Schroeter
Am Donnerstag, 26. Juni 2008 01:56:23 schrieb Sheila Barthel:
> In the current Lustre manual (v. 1_12), section 3.2.2 is Lustre Tools.
> Section 21.3.2 is Calculating MDT Size, which includes an inode
> calculation example and does not refer to the MDS.
>
> http://manual.lustre.org/manual/LustreManual16_HTML/LustreTuning.html#50446
>384_pgfId-1291157
>
> Please clarify which Lustre manual version you are referring to.
LustreManual_1.6_man_v19.pdf .
Sorry for the noise if this has been corrected allready.
But still missing some infos about the MDS partition size.
What is the minium size needed for the MDS partition ?
Is it the same size as the MDS RAM size calculation in the lustre manual 820-3681 (may 2008) 3.4.1 ? So partition_size = RAM size ?
Heiko