[gpfsug-discuss] gpfs performance monitoring

Salvatore Di Nardo sdinardo at ebi.ac.uk
Thu Sep 4 11:43:36 BST 2014


On 04/09/14 01:50, Sven Oehme wrote:
> > Hello everybody,
>
> Hi
>
> > here i come here again, this time to ask some hint about how to 
> monitor GPFS.
> >
> > I know about mmpmon, but the issue with its "fs_io_s" and "io_s" is
> > that they return number based only on the request done in the
> > current host, so i have to run them on all the clients ( over 600
> > nodes) so its quite unpractical.  Instead i would like to know from
> > the servers whats going on, and i came across the vio_s statistics
> > wich are less documented and i dont know exacly what they mean.
> > There is also this script "/usr/lpp/mmfs/samples/vdisk/viostat" that
> > runs VIO_S.
> >
> > My problems with the output of this command:
> >  echo "vio_s" | /usr/lpp/mmfs/bin/mmpmon -r 1
> >
> > mmpmon> mmpmon node 10.7.28.2 name gss01a vio_s OK VIOPS per second
> > timestamp: 1409763206/477366
> > recovery group: *
> > declustered array: *
> > vdisk: *
> > client reads: 2584229
> > client short writes: 55299693
> > client medium writes: 190071
> > client promoted full track writes:      465145
> > client full track writes: 9249
> > flushed update writes: 4187708
> > flushed promoted full track writes: 123
> > migrate operations: 114
> > scrub operations: 450590
> > log writes: 28509602
> >
> > it sais "VIOPS per second", but they seem to me just counters as
> > every time i re-run the command, the numbers increase by a bit..
> > Can anyone confirm if those numbers are counter or if they are OPS/sec.
>
> the numbers are accumulative so everytime you run them they just show 
> the value since start (or last reset) time.
OK, you confirmed my toughts, thatks

>
> >
> > On a closer eye about i dont understand what most of thosevalues
> > mean. For example, what exacly are "flushed promoted full track 
> write" ??
> > I tried to find a documentation about this output , but could not
> > find any. can anyone point me a link where output of vio_s is explained?
> >
> > Another thing i dont understand about those numbers is if they are
> > just operations, or the number of blocks that was read/write/etc .
>
> its just operations and if i would explain what the numbers mean i 
> might confuse you even more because this is not what you are really 
> looking for.
> what you are looking for is what the client io's look like on the 
> Server side, while the VIO layer is the Server side to the disks, so 
> one lever lower than what you are looking for from what i could read 
> out of the description above.
No.. what I'm looking its exactly how the disks are busy to keep the 
requests. Obviously i'm not looking just that, but I feel the needs to 
monitor _*also*_ those things. Ill explain you why.

It happens when our storage is quite busy ( 180Gb/s of read/write ) that 
the FS start to be slowin normal /*cd*/ or /*ls*/ requests. This might 
be normal, but in those situation i want to know where the bottleneck 
is. Is the server CPU? Memory? Network? Spindles? knowing where the 
bottlenek is might help me to understand if we can tweak the system a 
bit more.

If its the CPU on the servers then there is no much to do beside 
replacing or add more servers.If its not the CPU, maybe more memory 
would help? Maybe its just the network that filled up? so i can add more 
links

Or if we reached the point there the bottleneck its the spindles, then 
there is no much point o look somethere else, we just reached the 
hardware limit..

Sometimes, it also happens that there is very low IO (10Gb/s ), almost 
no cpu usage on the servers but huge slownes ( ls can take 10 seconds).  
Why that happens? There is not much data ops , but we think there is a 
huge ammount of metadata ops. So what i want to know is if the metadata 
vdisks are busy or not. If this is our problem, could some SSD disks 
dedicated to metadata help?


In particular im, a bit puzzled with the design of our GSS storage.
Each recovery groups have 3 declustered arrays, and each declustered 
aray have 1 data and 1 metadata vdisk, but in the end both metadata and 
data vdisks use the same spindles. The problem that, its that I dont 
understand if we have a metadata bottleneck there. Maybe some SSD disks 
in a dedicated declustered array would perform much better, but this is 
just theory. I really would like to be able to monitor IO activities on 
the metadata vdisks.



>
>
> so the Layer you care about is the NSD Server layer, which sits on top 
> of the VIO layer (which is essentially the SW RAID Layer in GNR)
>
> > I'm asking that because if they are just ops, i don't know how much
> > they could be usefull. For example one write operation could eman
> > write 1 block or write a file of 100GB. If those are oprations,
> > there is a way to have the oupunt in bytes or blocks?
>
> there are multiple ways to get infos on the NSD layer, one would be to 
> use the dstat plugin (see /usr/lpp/mmfs/sample/util) but thats counts 
> again.

Counters its not a problem. I can collect them and create some graphs in 
a monitoring tool. I will check that.

>
> the alternative option is to use mmdiag --iohist. this shows you a 
> history of the last X numbers of io operations on either the client or 
> the server side like on a client :
>
> # mmdiag --iohist
>
> === mmdiag: iohist ===
>
> I/O history:
>
>  I/O start time RW    Buf type disk:sectorNum     nSec  time ms qTime 
> ms       RpcTimes ms  Type  Device/NSD ID         NSD server
> --------------- -- ----------- ----------------- -----  ------- 
> -------- -----------------  ---- ------------------ ---------------
> 14:25:22.169617  R  LLIndBlock    1:1075622848      64   13.073   
>  0.000   12.959  0.063  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:22.182723  R       inode    1:1071252480       8    6.970  0.000 
>    6.908    0.038  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:53.659918  R  LLIndBlock    1:1081202176      64    8.309   
>  0.000    8.210    0.046  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:53.668262  R       inode    2:1081373696       8   14.117   
>  0.000   14.032    0.058  cli   C0A70402:53BEEA5E   192.167.4.2
> 14:25:53.682750  R  LLIndBlock    1:1065508736      64    9.254   
>  0.000    9.180    0.038  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:53.692019  R       inode    2:1064356608       8   14.899   
>  0.000   14.847    0.029  cli   C0A70402:53BEEA5E   192.167.4.2
> 14:25:53.707100  R       inode    2:1077830152       8   16.499   
>  0.000   16.449    0.025  cli   C0A70402:53BEEA5E   192.167.4.2
> 14:25:53.723788  R  LLIndBlock    1:1081202432      64    4.280   
>  0.000    4.203    0.040  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:53.728082  R       inode    2:1081918976       8    7.760  0.000 
>    7.710    0.027  cli   C0A70402:53BEEA5E     192.167.4.2
> 14:25:57.877416  R    metadata  2:678978560       16   13.343    0.000 
>   13.254    0.053  cli   C0A70402:53BEEA5E   192.167.4.2
> 14:25:57.891048  R  LLIndBlock    1:1065508608      64   15.491   
>  0.000   15.401  0.058  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:57.906556  R       inode    2:1083476520       8   11.723   
>  0.000   11.676    0.029  cli   C0A70402:53BEEA5E   192.167.4.2
> 14:25:57.918516  R  LLIndBlock    1:1075622720      64    8.062   
>  0.000    8.001    0.032  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:57.926592  R       inode    1:1076503480       8    8.087  0.000 
>    8.043    0.026  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:57.934856  R  LLIndBlock    1:1071088512      64    6.572   
>  0.000    6.510    0.033  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:57.941441  R       inode    2:1069885984       8   11.686   
>  0.000   11.641    0.024  cli   C0A70402:53BEEA5E   192.167.4.2
> 14:25:57.953294  R       inode    2:1083476936       8    8.951  0.000 
>    8.912    0.021  cli   C0A70402:53BEEA5E     192.167.4.2
> 14:25:57.965475  R       inode    1:1076503504       8    0.477  0.000 
>    0.053    0.000  cli   C0A70401:53BEEA7F     192.167.4.1
> 14:25:57.965755  R       inode    2:1083476488       8    0.410  0.000 
>    0.061    0.321  cli   C0A70402:53BEEA5E     192.167.4.2
> 14:25:57.965787  R       inode    2:1083476512       8    0.439  0.000 
>    0.053    0.342  cli   C0A70402:53BEEA5E     192.167.4.2
>
> you basically see if its a inode , data block , what size it has (in 
> sectors) , which nsd server you did send this request to, etc.
>
> on the Server side you see the type , which physical disk it goes to 
> and also what size of disk i/o it causes like :
>
> 14:26:50.129995  R       inode   12:3211886376      64   14.261   
>  0.000    0.000    0.000  pd   sdis
> 14:26:50.137102  R       inode   19:3003969520      64    9.004   
>  0.000    0.000    0.000  pd   sdad
> 14:26:50.136116  R       inode   55:3591710992      64   11.057   
>  0.000    0.000    0.000  pd   sdoh
> 14:26:50.141510  R       inode   21:3066810504      64    5.909   
>  0.000    0.000    0.000  pd   sdaf
> 14:26:50.130529  R       inode   89:2962370072      64   17.437   
>  0.000    0.000    0.000  pd   sddi
> 14:26:50.131063  R       inode   78:1889457000      64   17.062   
>  0.000    0.000    0.000  pd   sdsj
> 14:26:50.143403  R       inode   36:3323035688      64    4.807   
>  0.000    0.000    0.000  pd   sdmw
> 14:26:50.131044  R       inode   37:2513579736     128   17.181   
>  0.000    0.000    0.000  pd   sddv
> 14:26:50.138181  R       inode   72:3868810400      64   10.951   
>  0.000    0.000    0.000  pd   sdbz
> 14:26:50.138188  R       inode  131:2443484784     128   11.792   
>  0.000    0.000    0.000  pd   sdug
> 14:26:50.138003  R       inode  102:3696843872      64   11.994   
>  0.000    0.000    0.000  pd   sdgp
> 14:26:50.137099  R       inode  145:3370922504      64   13.225   
>  0.000    0.000    0.000  pd   sdmi
> 14:26:50.141576  R       inode   62:2668579904      64    9.313   
>  0.000    0.000    0.000  pd   sdou
> 14:26:50.134689  R       inode  159:2786164648      64   16.577   
>  0.000    0.000    0.000  pd   sdpq
> 14:26:50.145034  R       inode   34:2097217320      64    7.409   
>  0.000    0.000    0.000  pd   sdmt
> 14:26:50.138140  R       inode  139:2831038792      64   14.898   
>  0.000    0.000    0.000  pd   sdlw
> 14:26:50.130954  R       inode  164:282120312       64   22.274   
>  0.000    0.000    0.000  pd   sdzd
> 14:26:50.137038  R       inode   41:3421909608      64   16.314   
>  0.000    0.000    0.000  pd   sdef
> 14:26:50.137606  R       inode  104:1870962416      64   16.644   
>  0.000    0.000    0.000  pd   sdgx
> 14:26:50.141306  R       inode   65:2276184264      64   16.593   
>  0.000    0.000    0.000  pd   sdrk
>
>

mmdiag --iohist its another think i looked at it, but i could not find 
good explanation for all the "buf type" ( third column )

            allocSeg
            data
            iallocSeg
            indBlock
            inode
            LLIndBlock
            logData
            logDesc
            logWrap
            metadata
            vdiskAULog
            vdiskBuf
            vdiskFWLog
            vdiskMDLog
            vdiskMeta
            vdiskRGDesc

If i want to monifor metadata operation whan should i look at? just the 
metadata flag or also inode? this command takes also long to run, 
especially if i run it a second time it hangs for a lot before to rerun 
again, so i'm not sure that run it every 30secs or minute its viable, 
but i will look also into that. THere is any documentation that descibes 
clearly the whole output? what i found its quite generic and don't go 
into details...

> >
> > Last but not least.. and this is what i really would like to
> > accomplish, i would to be able to monitor the latency of metadata 
> operations.
>
> you can't do this on the server side as you don't know how much time 
> you spend on the client , network or anything between the app and the 
> physical disk, so you can only reliably look at this from the client, 
> the iohist output only shows you the Server disk i/o processing time, 
> but that can be a fraction of the overall time (in other cases this 
> obviously can also be the dominant part depending on your workload).
>
> the easiest way on the client is to run
>
> mmfsadm vfsstats enable
> from now on vfs stats are collected until you restart GPFS.
>
> then run :
>
> vfs statistics currently enabled
> started at: Fri Aug 29 13:15:05.380 2014
>   duration: 448446.970 sec
>
>  name        calls  time per call     total time
>  -------------------- -------- -------------- --------------
>  statfs          9       0.000002     0.000021
>  startIO  246191176       0.005853 1441049.976740
>
> to dump what ever you collected so far on this node.
>

We already do that, but as I said, I want to check specifically how gss 
servers are keeping the requests to identify or exlude server side 
bottlenecks.


Thanks for your help, you gave me definitely few things where to look at.

Salvatore

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