https://bugzilla.kernel.org/show_bug.cgi?id=21772
Summary: Poor Random Performance via NFS with Mixed Workload on
mdadm RAID-0
Product: File System
Version: 2.5
Kernel Version: 2.6.26 to 2.6.35
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: XFS
AssignedTo: xfs-masters@xxxxxxxxxxx
ReportedBy: pearce_jj@xxxxxxxxxxx
Regression: No
Configuration:
- Three disks sd[bcd]
- mdadm 3.1.5 providing RAID-0 device /dev/md0 on these (partitionless)
- XFS file system created on /dev/md0 and mounted on /mnt/v1
- NFS export created (rw,no_root_squash,async,noatime) for /mnt/v1
- VMware ESXi connectd to NFS export via dedicated GbE
- Windows 2003 Server guest on ESXi with volume on the NFS datastore
- Aligned partition created in guest
- IOMeter used to measure performance thus:
- 8K random, 4K aligned, 16 outstanding IOs, 8GB test file, 5 minute duration
Results:
- 100% read test performs as expected (c.1200 IOPS)
- 100% write test performs as expected (c.1200 IOPS)
- 70% read 30% write test performs badly c.400 IOPS
Monitoring the disks using iostat -xk /dev/sd[bcd] 5 60 during this test I note
that the queue depth is at or close to 1 for each disk in the mixed read/write
workload. For either 100% read or 100% write, the queue depth is as expected,
in line with the IOMeter test parameters.
The same results are obtained using Debian (2.6.26), Ubuntu 10.10 (2.6.35) and
Fedora 8 (2.6.26).
Reason for Bug Filing:
Using JFS, ext3 or ext4 instead of XFS in this configuration, the mixed
workload slow-down is not observed (and iostat in those cases shows no queue
depth throttling). The effect is not present operating direcly with a single
device (i.e. without mdadm).
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