On 1/28/2015 11:07 PM, John R Pierce wrote:> On 1/28/2015 4:32 AM, Jatin Davey wrote: >> I am using RHEL 6.5 on my server. >> >> From top command i can see that the processors in my server are >> spending a lot of time on wait for I/O. >> I can see high percentage in terms of 30-50% on "wa" time. >> >> Here is the df output about the disk space in my system: >> >> ********** >> [root at localhost images]# df >> Filesystem 1K-blocks Used Available Use% Mounted on >> /dev/sda1 1915071844 103227908 1714563936 6% / >> tmpfs 32931472 0 32931472 0% /dev/shm >> ********** >> >> Could someone point me on how to improve the disk I/O on my server >> and reduce the wait time on I/O. > > it appears you have everything on a single file system on a single 2TB > drive?[Jatin] Yes , entire disk is mounted on a single file system. Will this cause high wait time for I/O operations ? Do you think splitting it into multiple partitions would help ? Appreciate if you can enlighten me in this regard or provide pointers to it.> I'm going to guess thats a desktop grade SATA disk spinning at most at > 7200rpm (many are slower, 'green' disks are often 5400rpm).[Jatin] Yes , it is a SATA disk. I am not sure of the speed. Can you tell me how to find out this information ? Additionally we are using RAID 10 configuration with 4 disks.> > what sort of workload are you running?[Jatin] Our workload is a bit high on disk reads / writes and hence i am seeing slowness in it when using the top command. We basically run VMs on the RHEL 6.5 host. Our target is to house 5-6 application VMs on this host and ship this as a product on a rack server.> our high disk IO servers, doing things like transactional databases, > have many 10000rpm or 15000 rpm drives on a SAS2 raid card with 1GB or > 2GB of write-back-cache (battery or flash backed). > >Hi John Please see my responses inline. Appreciate your inputs in this regard. Thanks Jatin
On Thu, Jan 29, 2015 at 7:07 AM, Jatin Davey <jashokda at cisco.com> wrote:> > [Jatin] > Yes , entire disk is mounted on a single file system. Will this cause high > wait time for I/O operations ? Do you think splitting it into multiple > partitions would help ? Appreciate if you can enlighten me in this regard or > provide pointers to it.The extra time goes to move the head back and forth from one file to the next as different applications write to different files. Different partitions may make things even worse if they happen to force those locations to be farther apart. What you need are more drives with activity spread over them so you have a better chance of a head being near where it needs to be. Adding RAM can help to a certain extent by allowing more buffering. Faster disks will help too, but won't magically eliminate seek time - moving heads is still going to be your slowest computer operation.> [Jatin] > Our workload is a bit high on disk reads / writes and hence i am seeing > slowness in it when using the top command. We basically run VMs on the RHEL > 6.5 host. Our target is to house 5-6 application VMs on this host and ship > this as a product on a rack server.You can micro-manage this by putting a VM image on its own drive so you don't lose seek time between the images. Or make a raid with a very large number of members and hope the odds work out. -- Les Mikesell lesmikesell at gmail.com
On 01/29/2015 05:07 AM, Jatin Davey wrote:> Yes , it is a SATA disk. I am not sure of the speed. Can you tell me > how to find out this information ? Additionally we are using RAID 10 > configuration with 4 disks.What RAID controller are you using? # lspci | grep RAID
On 1/30/2015 1:53 AM, Gordon Messmer wrote:> On 01/29/2015 05:07 AM, Jatin Davey wrote: >> Yes , it is a SATA disk. I am not sure of the speed. Can you tell me >> how to find out this information ? Additionally we are using RAID 10 >> configuration with 4 disks. > > What RAID controller are you using? > > # lspci | grep RAID[Jatin] [root at localhost ~]# lspci | grep RAID 05:00.0 RAID bus controller: LSI Logic / Symbios Logic MegaRAID SAS-3 3108 [Invader] (rev 02)> > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos >