Hi Kevin, I think it will take time before I get a chance to have 5 drives in the same server, so I will see at that time to test RAID5.
I'm going to add one drive per server today or tomorrow to try to improve that. What IOPs should I try to have? 100? Less? It will all be SATA3 drives and I will configure all in RAID0. It doesn't seems to me to be an issue to lose one node, since data will be replicated everywhere else. I will "simply" have to replace the failing disk and restart the node, no? JM 2013/2/8, Kevin O'dell <[email protected]>: > 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 >> > >> for few more minutes to get some more data ... >> > >> >> > >> JM >> > >> >> > >> >> > >> 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 >> > >> looking >> > >> > at bringing in a second drive to help distribute the load? In >> > >> > your >> > >> testing >> > >> > 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 >> > >> what >> > >> > 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 >> > >> > TPS(IOPs) count that you are seeing? >> > >> > >> > >> > On Thu, Feb 7, 2013 at 9:00 PM, Jean-Marc Spaggiari >> > >> > <[email protected] >> > >> >> wrote: >> > >> > >> > >> >> Hi Kevin, >> > >> >> >> > >> >> I'm facing some issues on one of my nodes and I'm trying to find >> > >> >> a >> > way >> > >> >> to fix that. CPU is used about 10% by user, and 80% for WIO. So >> > >> >> I'm >> > >> >> looking for a way to improve that. The mother board can do RAIDx >> and >> > >> >> JBOD too. It's the server I used few weeks ago to run some disks >> > >> >> benchs. >> > >> >> >> > >> >> http://www.spaggiari.org/index.php/hbase/hard-drives-performances >> > >> >> >> > >> >> The conclusion was that RAID0 was 70% faster than JBOD. But JBOD >> was >> > >> >> faster than RAID1. >> > >> >> >> > >> >> I have a 2TB drive in this server and was thinking about just >> adding >> > >> >> another 2TB drive. >> > >> >> >> > >> >> What are the advantages of JBOD compared to RAID0? From the last >> > tests >> > >> >> I did, it was slower. >> > >> >> >> > >> >> Since I will have to re-format the disks anyway, I can re-run the >> > >> >> tests just in case I did not configured something properly.... >> > >> >> >> > >> >> JM >> > >> >> >> > >> >> 2013/2/7, Kevin O'dell <[email protected]>: >> > >> >> > Hey JM, >> > >> >> > >> > >> >> > Why RAID0? That has a lot of disadvantages to using a JBOD >> > >> >> > configuration? Wait I/O is a symptom, not a problem. Are you >> > >> actually >> > >> >> > experiencing a problem or are you treating for something you >> think >> > >> >> > should >> > >> >> > be lower? >> > >> >> > >> > >> >> > On Thu, Feb 7, 2013 at 8:19 PM, Jean-Marc Spaggiari >> > >> >> > <[email protected] >> > >> >> >> wrote: >> > >> >> > >> > >> >> >> Hi, >> > >> >> >> >> > >> >> >> What is an acceptable CPU_WIO % while running an heavy MR job? >> > >> >> >> Should >> > >> >> >> we also try to keep that under 10%? Or it's not realistic and >> > >> >> >> we >> > >> >> >> will >> > >> >> >> see more about 50%? >> > >> >> >> >> > >> >> >> One of my nodes is showing 70% :( It's WAY to much. I will add >> > >> another >> > >> >> >> disk tomorrow and put them in RAID0, but I'm wondering how low >> > >> >> >> shoud >> > >> I >> > >> >> >> go? >> > >> >> >> >> > >> >> >> JM >> > >> >> >> >> > >> >> > >> > >> >> > >> > >> >> > >> > >> >> > -- >> > >> >> > Kevin O'Dell >> > >> >> > Customer Operations Engineer, Cloudera >> > >> >> > >> > >> >> >> > >> > >> > >> > >> > >> > >> > >> > -- >> > >> > Kevin O'Dell >> > >> > Customer Operations Engineer, Cloudera >> > >> > >> > >> >> > > >> > > >> > > >> > > -- >> > > Kevin O'Dell >> > > Customer Operations Engineer, Cloudera >> > > >> > >> > > > > -- > Kevin O'Dell > Customer Operations Engineer, Cloudera >
