[gpfsug-discuss] Metadata only system pool
Uwe Falke
UWEFALKE at de.ibm.com
Tue Jan 23 20:35:56 GMT 2018
Hi, Kevin,
(reproducing mainly what I've learned from Yuri)
a 512B inode can hold about 32 Disk Addresses (DAs) addressing 32 physical
disk blocks (but mind: if max replication - not necessarily actual repl.
-- is set to more than 1, that mans for example 16 logical blocks (R=2). A
DA is 12 bytes. With a 4k inode you can expect the other 3.5kiB to contain
also DAs throughout (about 298)
So with R=2 (even if actual replication is r=1), a 4k inode can hold max
about 330 DAs addressing 165 logical blocks
The max file size w/out indirect addressing is thus 165 x blocksize (e.g.
1320MiB @8MiB)
However, there could be other data structures in an inode (EAs) reducing
the space available for DAs
Hence, YMMV
Mit freundlichen Grüßen / Kind regards
Dr. Uwe Falke
IT Specialist
High Performance Computing Services / Integrated Technology Services /
Data Center Services
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From: "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 01/23/2018 08:26 PM
Subject: Re: [gpfsug-discuss] Metadata only system pool
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi All,
This is all making sense and I appreciate everyone?s responses ? and again
I apologize for not thinking about the indirect blocks.
Marc - we specifically chose 4K inodes when we created this filesystem a
little over a year ago so that small files could fit in the inode and
therefore be stored on the metadata SSDs.
This is more of a curiosity question ? is it documented somewhere how a 4K
inode is used? I understand that for very small files up to 3.5K of that
can be for data, but what about for large files? I.e., how much of that
4K is used for block addresses (3.5K plus whatever portion was already
allocated to block addresses??) ? or what I?m really asking is, given 4K
inodes and a 1M block size how big does a file have to be before it will
need to use indirect blocks?
Thanks again?
Kevin
On Jan 23, 2018, at 1:12 PM, Marc A Kaplan <makaplan at us.ibm.com> wrote:
If one were starting over, it might make sense to use a smaller inode
size. I believe we still support 512, 1K, 2K.
Tradeoff with the fact that inodes can store data and EAs.
From: "Uwe Falke" <UWEFALKE at de.ibm.com>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 01/23/2018 04:04 PM
Subject: Re: [gpfsug-discuss] Metadata only system pool
Sent by: gpfsug-discuss-bounces at spectrumscale.org
rough calculation (assuming 4k inodes):
350 x 10^6 x 4096 Bytes=1.434TB=1.304TiB. With replication that uses
2.877TB or 2.308TiB
As already mentioned here, directory and indirect blocks come on top. Even
if you could get rid of a portion of the allocated and unused inodes that
metadata pool appears bit small to me.
If that is a large filesystem there should be some funding to extend it.
If you have such a many-but-small-files system as discussed recently in
this theatre, you might still beg for more MD storage but that makes than
a larger portion of the total cost (assuming data storage is on HDD and md
storage on SSD) and that again reduces your chances.
Mit freundlichen Grüßen / Kind regards
Dr. Uwe Falke
IT Specialist
High Performance Computing Services / Integrated Technology Services /
Data Center Services
-------------------------------------------------------------------------------------------------------------------------------------------
IBM Deutschland
Rathausstr. 7
09111 Chemnitz
Phone: +49 371 6978 2165
Mobile: +49 175 575 2877
E-Mail: uwefalke at de.ibm.com
-------------------------------------------------------------------------------------------------------------------------------------------
IBM Deutschland Business & Technology Services GmbH / Geschäftsführung:
Thomas Wolter, Sven Schooß
Sitz der Gesellschaft: Ehningen / Registergericht: Amtsgericht Stuttgart,
HRB 17122
From: "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 01/23/2018 06:17 PM
Subject: [gpfsug-discuss] Metadata only system pool
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi All,
I was under the (possibly false) impression that if you have a filesystem
where the system pool contains metadata only then the only thing that
would cause the amount of free space in that pool to change is the
creation of more inodes ? is that correct? In other words, given that I
have a filesystem with 130 million free (but allocated) inodes:
Inode Information
-----------------
Number of used inodes: 218635454
Number of free inodes: 131364674
Number of allocated inodes: 350000128
Maximum number of inodes: 350000128
I would not expect that a user creating a few hundred or thousands of
files could cause a ?no space left on device? error (which I?ve got one
user getting). There?s plenty of free data space, BTW.
Now my system pool is almost ?full?:
(pool total) 2.878T 34M ( 0%)
140.9M ( 0%)
But again, what - outside of me creating more inodes - would cause that to
change??
Thanks?
Kevin
?
Kevin Buterbaugh - Senior System Administrator
Vanderbilt University - Advanced Computing Center for Research and
Education
Kevin.Buterbaugh at vanderbilt.edu - (615)875-9633
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