[gpfsug-discuss] Write performances and filesystem size
Ivano Talamo
Ivano.Talamo at psi.ch
Thu Nov 16 08:44:06 GMT 2017
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,
Ivano
Il 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" <janfrode at tanso.net>
> An: "gpfsug main discussion list" <gpfsug-discuss at spectrumscale.org>
> 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 <olaf.weiser at de.ibm.com
> <mailto:olaf.weiser at de.ibm.com>>:
>
> 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" <kums at us.ibm.com
> <mailto:kums at us.ibm.com>>
> To: gpfsug main discussion list
> <gpfsug-discuss at spectrumscale.org
> <mailto:gpfsug-discuss at spectrumscale.org>>
> Date: 11/15/2017 11:56 AM
> Subject: Re: [gpfsug-discuss] Write performances and
> filesystem size
> Sent by: gpfsug-discuss-bounces at spectrumscale.org
> <mailto:gpfsug-discuss-bounces at spectrumscale.org>
> ------------------------------------------------------------------------
>
>
>
> 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 <Ivano.Talamo at psi.ch
> <mailto:Ivano.Talamo at psi.ch>>
> To: <gpfsug-discuss at spectrumscale.org
> <mailto:gpfsug-discuss at spectrumscale.org>>
> Date: 11/15/2017 11:25 AM
> Subject: [gpfsug-discuss] Write performances and filesystem size
> Sent by: gpfsug-discuss-bounces at spectrumscale.org
> <mailto:gpfsug-discuss-bounces at spectrumscale.org>
> ------------------------------------------------------------------------
>
>
>
> 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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