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HBase, mail # user - Acceptable CPU_WIO % ?


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Re: Acceptable CPU_WIO % ?
Kevin O'dell 2013-02-08, 13:56
Azuryy,

  The main reason to recommend against RAID is that it is slow and it adds
redundancy that we already have in Hadoop.  RAID0 is another story as long
as all of the drives are healthy and you don't mind losing the whole volume
if you lose one drive.

JM,

  I would not even waste my time testing RAID5 or RAID6(unless it is just
for educational purposes :) ).  200+ IOPs consistently on one SATA drive is
pretty high, that would explain your high I/O wait time.  If your use case
allows for you to lose the whole node, there is not a good reason for you
to shy away from RAID0.  Please let us know how this plays out with your
environment.

On Thu, Feb 7, 2013 at 10:23 PM, Azuryy Yu <[EMAIL PROTECTED]> wrote:

> JM,
>
> I don't have the context, but if you are using Hadoop/Hbase, so don't do
> RAID on your disk.
>
>
> On Fri, Feb 8, 2013 at 11:15 AM, Jean-Marc Spaggiari <
> [EMAIL PROTECTED]> wrote:
>
> > Ok. I see. For my usecase I prefer to loose the data and have faster
> > process. So I will go for RAID0 and keep the replication factor to
> > 3... If at some point I have 5 disks in the node, I will most probably
> > give a try to RAID5 and see the performances compared to the other
> > RAID/JBOD options.
> >
> > Is there a "rule", like, 1 HD per core? Or we can't really simplify that
> > much?
> >
> > So far I have that in the sar output:
> > 21:35:03          tps      rtps      wtps   bread/s   bwrtn/s
> > 21:45:03       218,85    215,97      2,88  45441,95    308,04
> > 21:55:02       209,73    206,67      3,06  43985,28    378,32
> > 22:05:04       215,03    211,71      3,33  44831,00    312,95
> > Average :      214,54    211,45      3,09  44753,09    333,07
> >
> > But I'm not sure what it means. I will wait for tomorrow to get more
> > results, but my job will be done over night, so I'm not sure the
> > average will be accurate...
> >
> > JM
> >
> >
> > 2013/2/7, Kevin O'dell <[EMAIL PROTECTED]>:
> > > JM,
> > >
> > >   I think you misunderstood me.  I am not advocating any form of RAID
> for
> > > Hadoop.  It is true that we already have redundancy built in with HDFS.
> >  So
> > > unless you were going to do something silly like sacrifice speed to run
> > > RAID1 or RAID5 and lower your replication to 2...just don't do it :)
> > >  Anyway, yes you probably should have 3 - 4 drives per node if not
> more.
> > >  At that point then the you will really see the benefit of JBOD over
> > RAID0
> > >
> > > Do you want to be able to lose a drive and keep the node up?  If yes,
> > then
> > > JBOD is for you.  Do you not care if you lose that node due to drive
> > > failure? You just need speed, then RAID0 may be the correct choice.
>  Sar
> > > will take some time to populate.  Give it about 24 hours and you should
> > be
> > > able to glean some interesting information.
> > >
> > > On Thu, Feb 7, 2013 at 9:50 PM, Jean-Marc Spaggiari
> > > <[EMAIL PROTECTED]
> > >> wrote:
> > >
> > >> Ok. I see with RAID0 might be better for me compare to JBOD. Also, why
> > >> do we want to use RAID1 or RAID5? We already have the redundancy done
> > >> by hadoop, is it not going to add another non-required level of
> > >> redundancy?
> > >>
> > >> Should I already think to have 3 or even 4 drives in each node?
> > >>
> > >> I tried sar -A and it's only giving me 2 lines.
> > >> root@node7:/home/hbase# sar -A
> > >> Linux 3.2.0-4-amd64 (node7)     2013-02-07      _x86_64_        (4
> CPU)
> > >>
> > >> 21:29:54          LINUX RESTART
> > >>
> > >> It was not enabled, so I just enabled it and restart sysstat, but
> > >> seems that it's still not populated.
> > >>
> > >> I have the diskstats plugin installed on ganglia, so I have a LOT of
> > >> disks information, but not this specific one.
> > >>
> > >> My write_bytes_per_sec is pretty low. Average is 232K for the last 2
> > >> hours. But my erad_bytes_per_sec is avera 22.83M for the same period.
> > >> The graph is looking like a comb.
> > >>
> > >> I just retried sar and some data is coming.. I will need to let it run

Kevin O'Dell
Customer Operations Engineer, Cloudera