Jean-Marc Spaggiari 2013-02-08, 01:19
Kevin Odell 2013-02-08, 01:43
Jean-Marc Spaggiari 2013-02-08, 02:00
Kevin Odell 2013-02-08, 02:21
Jean-Marc Spaggiari 2013-02-08, 02:50
Kevin Odell 2013-02-08, 02:57
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
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...
2013/2/7, Kevin O'dell <[EMAIL PROTECTED]>:
> 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]
>> 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
>> 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
>> for few more minutes to get some more data ...
>> 2013/2/7, Kevin O'dell <[EMAIL PROTECTED]>:
>> > JM,
>> > Okay, I think I see what was happening. You currently only have one
>> > drive in the system that is showing High I/O wait correct? You are
>> > at bringing in a second drive to help distribute the load? In your
>> > with two drives you saw that RAID0 offerred superior performance vs
>> > JBOD.
>> > Typically when we see RAID vs JBOD we are dealing with about 6 - 12
>> > drives. Here are some of the pluses and minuses:
>> > RAID0 - faster performance since the data is striped, but you are as
>> > fast
>> > as your slowest drive and one drive failure you lose the whole volume.
>> > JBOD - Better redundancy and faster than a RAID1, or a RAID5
>> > configuration(unsure about a RAID4), but you are slower than RAID0
>> > It sounds like since you only have 1 drive in the node right now, you
>> > wouldn't be gaining or losing any redundancy by going with RAID0. For
>> > it is worth, I would agree that you are I/O bound. If you run a sar -A
>> > >
>> > /tmp/sar.out and you take a look at the drive utilization what is your
Azuryy Yu 2013-02-08, 03:23
Kevin Odell 2013-02-08, 13:56
Jean-Marc Spaggiari 2013-02-08, 15:43
Kevin Odell 2013-02-08, 16:37
Jean-Marc Spaggiari 2013-02-09, 16:13