Rjx, that makes it a bit clearer.. as your vdisk is big enough to span over
all pdisks in each of your test 1/1 or 1/2 or 1/4 of capacity... should bring
the same performance. ..
You mean something about vdisk Layout. ..
So in your test, for the full capacity test, you use just one vdisk per RG -
so 2 in total for 'data' - right?
What about Md .. did you create separate vdisk for MD / what size then ?
Gesendet von IBM Verse
Ivano Talamo --- Re: [gpfsug-discuss] Write performances and filesystem size
---
Von:"Ivano Talamo" <[email protected]>An:"gpfsug main discussion list"
<[email protected]>Datum:Do. 16.11.2017 03:49Betreff:Re:
[gpfsug-discuss] Write performances and filesystem size
Hello Olaf,yes, I confirm that is the Lenovo version of the ESS GL2, so 2
enclosures/4 drawers/166 disks in total.Each recovery group has one declustered
array with all disks inside, so vdisks use all the physical ones, even in the
case of a vdisk that is 1/4 of the total size.Regarding the layout allocation
we used scatter.The tests were done on the just created filesystem, so no
close-to-full effect. And we run gpfsperf write seq.Thanks,IvanoIl 16/11/17
04:42, Olaf Weiser ha scritto:> Sure... as long we assume that really all
physical disk are used .. the> fact that was told 1/2 or 1/4 might turn out
that one / two complet> enclosures 're eliminated ... ? ..that s why I was
asking for more> details ..>> I dont see this degration in my environments. .
as long the vdisks are> big enough to span over all pdisks ( which should be
the case for> capacity in a range of TB ) ... the performance stays the same>>
Gesendet von IBM Verse>> Jan-Frode Myklebust --- Re: [gpfsug-discuss] Write
performances and> filesystem size --->> Von: "Jan-Frode Myklebust"
<[email protected]>> An: "gpfsug main discussion list"
<[email protected]>> Datum: Mi. 15.11.2017 21:35> Betreff:
Re: [gpfsug-discuss] Write performances and filesystem size>>
------------------------------------------------------------------------>>
Olaf, this looks like a Lenovo «ESS GLxS» version. Should be using same> number
of spindles for any size filesystem, so I would also expect them> to perform
the same.>>>> -jf>>> ons. 15. nov. 2017 kl. 11:26 skrev Olaf Weiser
<[email protected]> <mailto:[email protected]>>:>> to add a
comment ... .. very simply... depending on how you> allocate the physical
block storage .... if you - simply - using> less physical resources when
reducing the capacity (in the same> ratio) .. you get , what you see....>>
so you need to tell us, how you allocate your block-storage .. (Do> you
using RAID controllers , where are your LUNs coming from, are> then less
RAID groups involved, when reducing the capacity ?...)>> GPFS can be
configured to give you pretty as much as what the> hardware can deliver..
if you reduce resource.. ... you'll get less> , if you enhance your
hardware .. you get more... almost regardless> of the total capacity in
#blocks ..>>>>>>> From: "Kumaran Rajaram" <[email protected]>
<mailto:[email protected]>>> To: gpfsug main discussion list>
<[email protected]>
<mailto:[email protected]>>> Date: 11/15/2017 11:56
AM> Subject: Re: [gpfsug-discuss] Write performances and>
filesystem size> Sent by: [email protected]>
<mailto:[email protected]>>
------------------------------------------------------------------------>>>>
Hi,>> >>Am I missing something? Is this an expected behaviour and someone>
has an explanation for this?>> Based on your scenario, write
degradation as the file-system is> populated is possible if you had
formatted the file-system with "-j> cluster".>> For consistent
file-system performance, we recommend *mmcrfs "-j> scatter" layoutMap.*
Also, we need to ensure the mmcrfs "-n" is> set properly.>> [snip from
mmcrfs]/> # mmlsfs <fs> | egrep 'Block allocation| Estimated number'>
-j scatter Block allocation type> -n
128 Estimated number of> nodes that will
mount file system/> [/snip]>>> [snip from man mmcrfs]/>
*layoutMap={scatter|*//*cluster}*//> Specifies the block
allocation map type. When> allocating blocks for a given
file, GPFS first> uses a round‐robin algorithm to spread
the data> across all disks in the storage pool. After a>
disk is selected, the location of the data>
block on the disk is determined by the block>
allocation map type*. If cluster is> specified, GPFS
attempts to allocate blocks in> clusters. Blocks that
belong to a particular> file are kept adjacent to each
other within> each cluster. If scatter is specified,>
the location of the block is chosen randomly.*/> />
* The cluster allocation method may provide>
better disk performance for some disk> subsystems in
relatively small installations.> The benefits of clustered
block allocation> diminish when the number of nodes in
the> cluster or the number of disks in a file system>
increases, or when the file system’s free space>
becomes fragmented. *//The *cluster*//> allocation
method is the default for GPFS> clusters with eight or
fewer nodes and for file> systems with eight or fewer
disks./> /> *The scatter allocation method provides>
more consistent file system performance by>
averaging out performance variations due to> block
location (for many disk subsystems, the> location of the
data relative to the disk edge> has a substantial effect
on performance).*//This> allocation method is appropriate
in most cases> and is the default for GPFS clusters with
more> than eight nodes or file systems with more than>
eight disks./> /> The block
allocation map type cannot be changed> after the storage
pool has been created./>> */> -n/*/*NumNodes*//> The
estimated number of nodes that will mount the file> system in the
local cluster and all remote clusters.> This is used as a best
guess for the initial size of> some file system data structures.
The default is 32.> This value can be changed after the file system
has been> created but it does not change the existing data>
structures. Only the newly created data structure is> affected
by the new value. For example, new storage> pool./> />
When you create a GPFS file system, you might want to>
overestimate the number of nodes that will mount the> file system.
GPFS uses this information for creating> data structures that are
essential for achieving maximum> parallelism in file system
operations (For more> information, see GPFS architecture in IBM
Spectrum> Scale: Concepts, Planning, and Installation Guide ). If>
you are sure there will never be more than 64 nodes,>
allow the default value to be applied. If you are> planning to add
nodes to your system, you should specify> a number larger than the
default./>> [/snip from man mmcrfs]>> Regards,> -Kums>>>>>>
From: Ivano Talamo <[email protected]>
<mailto:[email protected]>>> To:
<[email protected]>
<mailto:[email protected]>>> Date: 11/15/2017 11:25
AM> Subject: [gpfsug-discuss] Write performances and filesystem
size> Sent by: [email protected]>
<mailto:[email protected]>>
------------------------------------------------------------------------>>>>
Hello everybody,>> together with my colleagues we are actually running
some tests on a new> DSS G220 system and we see some unexpected
behaviour.>> What we actually see is that write performances (we did not
test read> yet) decreases with the decrease of filesystem size.>> I
will not go into the details of the tests, but here are some numbers:>> -
with a filesystem using the full 1.2 PB space we get 14 GB/s as the> sum of
the disk activity on the two IO servers;> - with a filesystem using half of
the space we get 10 GB/s;> - with a filesystem using 1/4 of the space we
get 5 GB/s.>> We also saw that performances are not affected by the vdisks
layout,> ie.> taking the full space with one big vdisk or 2 half-size
vdisks per RG> gives the same performances.>> To our understanding the
IO should be spread evenly across all the> pdisks in the declustered array,
and looking at iostat all disks> seem to> be accessed. But so there
must be some other element that affects> performances.>> Am I missing
something? Is this an expected behaviour and someone> has an>
explanation for this?>> Thank you,> Ivano>
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