JM, Basically, you will have to replace failed disk and rebuild RAID0 since the other half of the data is worthless. There is not a real recommended value, but anything under 150 - 200 would make me more comfortable.
On Fri, Feb 8, 2013 at 10:43 AM, Jean-Marc Spaggiari < [email protected]> wrote: > 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 > > > -- Kevin O'Dell Customer Operations Engineer, Cloudera
