MVSAS maxing out bandwidth at 2.5 Gbps

MVSAS maxing out bandwidth at 2.5 Gbps

[Audio Haven]

I have 8 Western Digital WD15EADS 1.5T green drives in a software
raid6 6+2 config using 1024K chunk size.
They are connected to a SuperMicro SASLP-MV8 card sitting in the 16x
PCI-E slot of an old but stable Asus K8N4E-Deluxe board.

Every single drive appears to read at >90Mbyte/sec:
hdparm -t /dev/sdb
 Timing buffered disk reads:  282 MB in  3.02 seconds =  93.49 MB/sec

But when I try to hdparm -t /dev/md2, I max out at around 180Mbyte/sec
and the read seems to be nicely distributed across all drives
according to iostat -k :

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           5.00    0.00   95.00    0.00    0.00    0.00

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               0.00         0.00         0.00          0          0
sdb             115.00     23552.00         0.00      23552          0
sdc             110.00     22528.00         0.00      22528          0
sdd             115.00     23552.00         0.00      23552          0
sde             115.00     23552.00         0.00      23552          0
sdf             113.00     23040.00         0.00      23040          0
sdg             112.00     23040.00         0.00      23040          0
sdh             119.00     24324.00         0.00      24324          0
sdi             121.00     24576.00         0.00      24576          0
md2           47783.00    191132.00         0.00     191132          0

sda is my boot drive connected to the onboard nforce, not part of the raidset

When loading the mvsas module, it seems the bandwith is limited:
mvsas 0000:01:00.0: mvsas: PCI-E x4, Bandwidth Usage: 2.5 Gbps

which seems strange as it should be able to do 250Mbyte/sec per lane,
so 4 lanes should amount to 1 Gbyte / sec even for the oldest PCI-E
v1.x standard.

My system is Fedora 12  x86_64 using a custom 2.6.32.3 kernel with the
following patches from Andy Yan:

[PATCH 6/7]MVSAS: Enhanced hot plug handling
[PATCH 5/7]MVSAS:Optimization for DMA buffer
[PATCH 4/7]MVSAS:Make code more flexibe for different chip model.
[PATCH 3/7]MVSAS: bug fix with big endian
[PATCH 2/7]MVSAS:add supporting MSI feature
[PATCH 1/7]MVSAS: Update chip initialization

I did not use [PATCH 7/7]

I can report these patches solved all of my raid6 stability issues
(drives kicking out of the raid, /proc/mdstat not reporting faults,
xfs corruption) and have been running stable for the past 3 weeks with
all sorts of stress testing.

Am I missing something with regards to tuning to get the full
bandwidth out of this marvell controller ?

Re: MVSAS maxing out bandwidth at 2.5 Gbps

[Caspar Smit]

Hi,

You say you stress tested this setup.
Can you tell me your experiences with hotplugging in combination with SATA
disks (which you are using). I seem to keep getting kernel panics when
hotplugging SATA disks with the same controller, kernel and patches you
mention.

I mentioned this (with several others in this mailinglist) some time ago
but no reaction since.

Kind regards,
Caspar Smit


> I have 8 Western Digital WD15EADS 1.5T green drives in a software
> raid6 6+2 config using 1024K chunk size.
> They are connected to a SuperMicro SASLP-MV8 card sitting in the 16x
> PCI-E slot of an old but stable Asus K8N4E-Deluxe board.
>
> Every single drive appears to read at >90Mbyte/sec:
> hdparm -t /dev/sdb
>  Timing buffered disk reads:  282 MB in  3.02 seconds =  93.49 MB/sec
>
> But when I try to hdparm -t /dev/md2, I max out at around 180Mbyte/sec
> and the read seems to be nicely distributed across all drives
> according to iostat -k :
>
> avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>            5.00    0.00   95.00    0.00    0.00    0.00
>
> Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
> sda               0.00         0.00         0.00          0          0
> sdb             115.00     23552.00         0.00      23552          0
> sdc             110.00     22528.00         0.00      22528          0
> sdd             115.00     23552.00         0.00      23552          0
> sde             115.00     23552.00         0.00      23552          0
> sdf             113.00     23040.00         0.00      23040          0
> sdg             112.00     23040.00         0.00      23040          0
> sdh             119.00     24324.00         0.00      24324          0
> sdi             121.00     24576.00         0.00      24576          0
> md2           47783.00    191132.00         0.00     191132          0
>
> sda is my boot drive connected to the onboard nforce, not part of the
> raidset
>
> When loading the mvsas module, it seems the bandwith is limited:
> mvsas 0000:01:00.0: mvsas: PCI-E x4, Bandwidth Usage: 2.5 Gbps
>
> which seems strange as it should be able to do 250Mbyte/sec per lane,
> so 4 lanes should amount to 1 Gbyte / sec even for the oldest PCI-E
> v1.x standard.
>
> My system is Fedora 12  x86_64 using a custom 2.6.32.3 kernel with the
> following patches from Andy Yan:
>
> [PATCH 6/7]MVSAS: Enhanced hot plug handling
> [PATCH 5/7]MVSAS:Optimization for DMA buffer
> [PATCH 4/7]MVSAS:Make code more flexibe for different chip model.
> [PATCH 3/7]MVSAS: bug fix with big endian
> [PATCH 2/7]MVSAS:add supporting MSI feature
> [PATCH 1/7]MVSAS: Update chip initialization
>
> I did not use [PATCH 7/7]
>
> I can report these patches solved all of my raid6 stability issues
> (drives kicking out of the raid, /proc/mdstat not reporting faults,
> xfs corruption) and have been running stable for the past 3 weeks with
> all sorts of stress testing.
>
> Am I missing something with regards to tuning to get the full
> bandwidth out of this marvell controller ?
> --
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