Write I/O Performance in Oracle VM Server for SPARC (LDoms) Guest Domains Degrades with High Average Service Time

(Doc ID 1628563.1)

Last updated on SEPTEMBER 13, 2017

Applies to:

Solaris Operating System - Version 10 1/13 U11 to 11.1 [Release 10.0 to 11.0]
Information in this document applies to any platform.

Symptoms

This issue can occur in the following releases:

SPARC Platform

 

If a ZVOL or a file on ZFS in the I/O domain(this can be either the control domain or service domain) is exported to a guest domain, write I/O performance in the guest domain can be seen degraded.

When this issue happens, user will observe poor I/O performance on the guest domain. At the same time, the user will not observe any I/O anomaly on the I/O domain.

 

In the following example, a ZVOL on the zpool in the I/O domain which is mirrored with c0t500001853210A5F0d0 and c0t50000185321076BCd0 is exported to the guest domain as c0d0.

/usr/bin/iostat -xpnC in the guest domain shows high asvc_t on c0d0:


If ZIL calls txg_wait_synced(), it means ZIL is failing to allocate a log write buffer. When this happens, synchronous write performance is severely degraded.

So, in this specific scenario, I/O performance in the guest domain is the direct result of issue in the ZIL layer in the I/O domain.

Cause

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