kern/110846: gmirror read speed is half of maximum

[Mykola Zubach]

>Number:         110846
>Category:       kern
>Synopsis:       gmirror read speed is half of maximum
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Mar 26 11:30:04 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Mykola Zubach
>Release:        FreeBSD-6.2
>Organization:
AdvancedHosters.com
>Environment:
FreeBSD A0022 6.2-RELEASE FreeBSD 6.2-RELEASE #2: Mon Jan 29 15:06:29 UTC 2007     root at A00014:/usr/src/sys/i386/compile/Z  i386

>Description:
Correct RAID1 (mirroring) implementation cause raw read speed to to be doubled compared to raw read speed from single drive. But gmirror doesn't:

A0022# gmirror list
Geom name: gm0
State: COMPLETE
Components: 2
Balance: round-robin
Slice: 4096
Flags: NOAUTOSYNC
GenID: 0
SyncID: 1
ID: 2775573558
Providers:
1. Name: mirror/gm0
   Mediasize: 250059349504 (233G)
   Sectorsize: 512
   Mode: r7w7e8
Consumers:
1. Name: ad4
   Mediasize: 250059350016 (233G)
   Sectorsize: 512
   Mode: r1w1e1
   State: ACTIVE
   Priority: 0
   Flags: DIRTY
   GenID: 0
   SyncID: 1
   ID: 3586241583
2. Name: ad6
   Mediasize: 250059350016 (233G)
   Sectorsize: 512
   Mode: r1w1e1
   State: ACTIVE
   Priority: 0
   Flags: DIRTY
   GenID: 0
   SyncID: 1
   ID: 787590598

Parralel read from HDDs test:

A0022# dd if=/dev/ad4 of=/dev/null bs=128k count=10000 & dd if=/dev/ad6 of=/dev/null bs=128k count=10000
[1] 58794
10000+0 records in
10000+0 records out
1310720000 bytes transferred in 15.590913 secs (84069483 bytes/sec)
10000+0 records in
10000+0 records out
1310720000 bytes transferred in 16.416866 secs (79839842 bytes/sec)

 L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
    1    608    608  77873    1.6      0      0    0.0   97.4| ad4
    1    616    616  78862    1.6      0      0    0.0   97.0| ad6

Read from gmirror test:

A0022# dd if=/dev/mirror/gm0 of=/dev/null bs=128k count=10000 
10000+0 records in
10000+0 records out
1310720000 bytes transferred in 16.624842 secs (78841050 bytes/sec)

 L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
    0    309    309  39553    1.1      0      0    0.0   33.0| ad4
    1    307    307  39306    2.0      0      0    0.0   62.8| ad6
    1    616    616  78859    1.6      0      0    0.0   96.9| mirror/gm0

>How-To-Repeat:
Setup gmirror on any harware components on any FreeBSD release
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: