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On DL380p gen8 servers using XFS on top of LVM on top of raid 1+0 with 6 disks, an identical workload results in a ten-fold increase in disk writes on RHEL 6 compared to RHEL 5, making applications unusable.

Note that I'm not looking at optimizing the co6 system as much as possible, but at understanding why co6 behaves so wildly different, and solving that.

vmstat/iostat

We have a MySQL replication setup, using mysql 5.5. Mysql slaves on gen8 servers using RHEL 6 as OS perform badly, inspection with vmstat and iostat shows that these servers do ten times the page out activity and ten times the amount of writes to the disk subsystem. blktrace show that these writes are not initiated by mysql, but by the kernel.

Centos 5:

[dkaarsemaker@co5 ~]$ vmstat 1
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 3  0     12 252668 102684 10816864    0    0     8   124    0    0  9  1 90  0  0
 1  0     12 251580 102692 10817116    0    0    48  2495 3619 5268  6  1 93  0  0
 3  0     12 252168 102692 10817848    0    0    32  2103 4323 5956  6  1 94  0  0
 3  0     12 252260 102700 10818672    0    0   128  5212 5365 8142 10  1 89  0  0

[dkaarsemaker@co5 ~]$ iostat 1
Linux 2.6.18-308.el5 (bc290bprdb-01.lhr4.prod.booking.com)  02/28/2013

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           8.74    0.00    0.81    0.25    0.00   90.21

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
cciss/c0d0      277.76       399.60      5952.53 2890574849 43058478233
cciss/c0d0p1      0.01         0.25         0.01    1802147      61862
cciss/c0d0p2      0.00         0.01         0.00     101334      32552
cciss/c0d0p3    277.75       399.34      5952.52 2888669185 43058383819
dm-0             32.50        15.00       256.41  108511602 1854809120
dm-1            270.24       322.97      5693.34 2336270565 41183532042

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           7.49    0.00    0.79    0.08    0.00   91.64

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
cciss/c0d0      300.00        32.00      4026.00         32       4026
cciss/c0d0p1      0.00         0.00         0.00          0          0
cciss/c0d0p2      0.00         0.00         0.00          0          0
cciss/c0d0p3    300.00        32.00      4026.00         32       4026
dm-0              0.00         0.00         0.00          0          0
dm-1            300.00        32.00      4026.00         32       4026

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           4.25    0.00    0.46    0.21    0.00   95.09

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
cciss/c0d0      507.00       160.00     10370.00        160      10370
cciss/c0d0p1      0.00         0.00         0.00          0          0
cciss/c0d0p2      0.00         0.00         0.00          0          0
cciss/c0d0p3    507.00       160.00     10370.00        160      10370
dm-0              0.00         0.00         0.00          0          0
dm-1            507.00       160.00     10370.00        160      10370

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           5.33    0.00    0.50    0.08    0.00   94.09

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
cciss/c0d0      318.00        64.00      4559.00         64       4559
cciss/c0d0p1      0.00         0.00         0.00          0          0
cciss/c0d0p2      0.00         0.00         0.00          0          0
cciss/c0d0p3    319.00        64.00      4561.00         64       4561
dm-0              0.00         0.00         0.00          0          0
dm-1            319.00        64.00      4561.00         64       4561

And on Centos 6 a ten-fold increase in paged out and disk writes:

[root@co6 ~]# vmstat 1
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 361044  52340 81965728    0    0    19  1804   36  110  1  1 98  0  0  
 0  0      0 358996  52340 81965808    0    0   272 57584 1211 3619  0  0 99  0  0  
 2  0      0 356176  52348 81966800    0    0   240 34128 2121 14017  1  0 98  0  0 
 0  1      0 351844  52364 81968848    0    0  1616 29128 3648 3985  1  1 97  1  0  
 0  0      0 353000  52364 81969296    0    0   480 44872 1441 3480  1  0 99  0  0  

[root@co6 ~]# iostat 1
Linux 2.6.32-279.22.1.el6.x86_64 (bc291bprdb-01.lhr4.prod.booking.com)  02/28/2013  _x86_64_    (32 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           1.08    0.00    0.67    0.27    0.00   97.98

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda             373.48      1203.02    115203.05   11343270 1086250748
dm-0             63.63        74.92       493.63     706418    4654464
dm-1            356.48      1126.72    114709.47   10623848 1081596740

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.25    0.00    0.19    0.06    0.00   99.50

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda             330.00        80.00     77976.00         80      77976
dm-0              0.00         0.00         0.00          0          0
dm-1            328.00        64.00     77456.00         64      77456

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.38    0.00    0.19    0.63    0.00   98.81

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda             570.00      1664.00    128120.00       1664     128120
dm-0              0.00         0.00         0.00          0          0
dm-1            570.00      1664.00    128120.00       1664     128120

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.66    0.00    0.47    0.03    0.00   98.84

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda             317.00       448.00     73048.00        448      73048
dm-0             34.00         0.00       272.00          0        272
dm-1            309.00       448.00     72776.00        448      72776

Narrowing down

Gen 8 servers using RHEL 5, and gen 7 servers using RHEL 5 or 6 do not show this problem. Furthermore, RHEL 6 with ext3 as filesystem instead of our default xfs does not show the problem. The problem really seems to be somewhere between XFS, gen8 hardware and centos 6. RHEL 6 also shows the problem.

Edit 29/04: we added qlogic HBA's t the G8 machine. Using XFS on fibre channel storage does not show the problem. So it's definitely somewhere in the interaction between xfs/hpsa/p420i.

XFS

The newer xfs in rhel 8 seems to be able to detect underlying stripe width, but only on p420i controllers using the hpsa driver, not p410i controllers using cciss.

xfs_info output:

[root@co6 ~]# xfs_info /mysql/bp/
meta-data=/dev/mapper/sysvm-mysqlVol isize=256    agcount=16, agsize=4915136 blks
         =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=78642176, imaxpct=25
         =                       sunit=64     swidth=192 blks
naming   =version 2              bsize=4096   ascii-ci=0
log      =internal               bsize=4096   blocks=38400, version=2
         =                       sectsz=512   sunit=64 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

sunit/swidth are both 0 in all the setup marked as OK above. We seem to be unable to change this, either in mkfs or with the noalign mount option. We also don't know if this is the cause.

Hugepages

Other people having XFS problems on rhel 6, say that disabling hugepages, and especially transparent hugepages can be beneficial. We disabled both, the problem did not go away.

We tried and observed many things already, none of the following have helped:

  • Using numactl to influence memory allocations. We noticed that g7 and g8 have a different numa layout, no effect was seen
  • Newer kernels (as new as 3.6) did not seem to solve this. Neither did using fedora 17.
  • iostat does not report a ten-fold increase in write transactions, only in number of bytes written
  • Using different I/O schedulers has no effect.
  • Mounting the relevant filesystem noatime/nobarrier/nopdiratime did not help
  • Changing /proc/sys/vm/dirty_ratio had no effect
  • This happens both on systems based on 2640 and 2670 CPU's
  • hpsa-3.2.0 doesn't fix the problem
share|improve this question
    
Show your XFS mkfs.xfs and mount options. EL6 is partition-alignment aware. HPSA would be in use for both Smart Array controller types under EL6, but EL5 would use CCISS. –  ewwhite Feb 28 '13 at 13:38
    
mkfs options: none. Mount line: /dev/mapper/sysvm-mysqlVol on /mysql/bp type xfs (rw,allocsize=1m). Will add full xfs_info output to the post. –  Dennis Kaarsemaker Feb 28 '13 at 13:55
    
So what was the solution? –  ewwhite Apr 22 at 21:59

2 Answers 2

XFS and EL6 have fallen into an ugly state... I've abandoned XFS on EL6 systems for the time being due to several upstream features/changes slipping into the Red Hat kernel...

This one was a surprise and caused some panic: Why are my XFS filesystems suddenly consuming more space and full of sparse files?

Since November 2012, the XFS version shipping in kernels newer than 2.6.32-279.11.1.el6 have an annoying load and performance issue stemming from Red Hat Bugzilla 860787. Since then, I've had unpredictable performance and higher run queues than average.

For new systems, I'm using ZFS or just ext4. For older systems, I'm freezing them at 2.6.32-279.11.1.el6.

Try rolling back to that version with:

yum install kernel-2.6.32-279.11.1.el6.x86_64

In addition to the above, due to the type of RAID controller you're using, the typical optimizations are in order:

Mount your XFS filesystems noatime. You should also leverage the Tuned framework with:

tuned-adm profile enterprise-storage

to set readahead, nobarrier and I/O elevator to a good baseline.


Edit:

There are plenty of recommendations surrounding XFS filesystem optimization. I've used the filesystem exclusively for the past decade and have had to occasionally adjust parameters as underlying changes to the operating system occurred. I have not experienced a dramatic performance decrease such as yours, but I also do not use LVM.

I think it's unreasonable to expect EL5 to act the same way as EL6, given the different kernel generation, compiled-in defaults, schedulers, packages, etc.

What would I do at this point??

  • I would examine the mkfs.xfs parameters and how you're building the systems. Are you using XFS partitioning during installation or creating the partitions after the fact? I do the XFS filesystem creation following the main OS installation because I have more flexibility in the given parameters.

  • My mkfs.xfs creation parameters are simple: mkfs.xfs -f -d agcount=32 -l size=128m,version=2 /dev/sdb1 for instance.

  • My mount options are: noatime,logbufs=8,logbsize=256k,nobarrier I would allow the XFS dynamic preallocation to run natively and not constrain it like you have here. My performance improved with it.

  • So I don't use LVM. Especially on top of hardware RAID... Especially on HP Smart Array controllers, where there are some LVM-like functions native to the device. However, using LVM, you don't have access to fdisk for raw partition creation. One thing that changed from EL5 to EL6 is the partition alignment in the installer and changes to fdisk to set the starting sector on a cylinder boundary.

  • Make sure you're running your HP Smart Array controllers and drives at the current revision level. At that point, it makes sense to update the entire server to the current HP Service Pack for ProLiant firmware revision. This is a bootable DVD that will upgrade all detected components in the system.

  • I'd check RAID controller settings. Pastebin the output of hpacucli ctrl all show config detail. Here's mine. You want a cache ratio biased towards writes versus reads. 75:25 is the norm. The default strip size of 256K should be fine for this application.

  • I'd potentially try this without LVM.

  • What are your sysctl.conf parameters?

share|improve this answer
    
Unfortunately, the older kernel shows the same behaviour. –  Dennis Kaarsemaker Feb 28 '13 at 14:00
    
Test without LVM. –  ewwhite Mar 3 '13 at 15:55

We had the similar issue, and found out it is due to XFS log version change. Version 2 logs honor the stripe width set used with mkfs.xfs. If you do a lot of fsync, your raid card can not fake those logs writes anymore. You may test it by format the partition without any swidth setting(it does not make any difference with RAID 1+0). You can verify that with blktrace/seekwatcher to see if it involves a lot of log update.

share|improve this answer
    
What's your mkfs.xfs command string? –  ewwhite Jun 19 at 19:37
    
I've been meaning to provide an answer myself, as we eventually did find it. Your answer is part of the solution, but not all of it. –  Dennis Kaarsemaker Jun 19 at 19:54
    
mkfs.xfs -f /your_dev –  mjiang Jun 19 at 20:12

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