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Subject: Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
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From: Ogden <lists@darkstatic.com>
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Date: Thu, 18 Aug 2011 12:31:28 -0500
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To: Greg Smith <greg@2ndquadrant.com>
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On Aug 17, 2011, at 4:17 PM, Greg Smith wrote:

> On 08/17/2011 02:26 PM, Ogden wrote:
>> I am using bonnie++ to benchmark our current Postgres system (on RAID =
5) with the new one we have, which I have configured with RAID 10. The =
drives are the same (SAS 15K). I tried the new system with ext3 and then =
XFS but the results seem really outrageous as compared to the current =
system, or am I reading things wrong?
>>=20
>> The benchmark results are here:
>> http://malekkoheavyindustry.com/benchmark.html
>=20
> Congratulations--you're now qualified to be a member of the "RAID5 =
sucks" club.  You can find other members at =
http://www.miracleas.com/BAARF/BAARF2.html  Reasonable read speeds and =
just terrible write ones are expected if that's on your old hardware.  =
Your new results are what I would expect from the hardware you've =
described.
>=20
> The only thing that looks weird are your ext4 "Sequential Output - =
Block" results.  They should be between the ext3 and the XFS results, =
not far lower than either.  Normally this only comes from using a bad =
set of mount options.  With a battery-backed write cache, you'd want to =
use "nobarrier" for example; if you didn't do that, that can crush =
output rates.


I have mounted the ext4 system with the nobarrier option:

/dev/sdb1 on /var/lib/pgsql type ext4 =
(rw,noatime,data=3Dwriteback,barrier=3D0,nobh,errors=3Dremount-ro)

Yet the results show absolutely a decrease in performance in the  ext4 =
"Sequential Output - Block" results:

http://malekkoheavyindustry.com/benchmark.html

However, the Random seeks is better, even more so than XFS...

Any thoughts as to why this is occurring?

Ogden



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<html><head></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =
"><br><div><div>On Aug 17, 2011, at 4:17 PM, Greg Smith wrote:</div><br =
class=3D"Apple-interchange-newline"><blockquote type=3D"cite"><div>On =
08/17/2011 02:26 PM, Ogden wrote:<br><blockquote type=3D"cite">I am =
using bonnie++ to benchmark our current Postgres system (on RAID 5) with =
the new one we have, which I have configured with RAID 10. The drives =
are the same (SAS 15K). I tried the new system with ext3 and then XFS =
but the results seem really outrageous as compared to the current =
system, or am I reading things wrong?<br></blockquote><blockquote =
type=3D"cite"><br></blockquote><blockquote type=3D"cite">The benchmark =
results are here:<br></blockquote><blockquote type=3D"cite"><a =
href=3D"http://malekkoheavyindustry.com/benchmark.html">http://malekkoheav=
yindustry.com/benchmark.html</a><br></blockquote><br>Congratulations--you'=
re now qualified to be a member of the "RAID5 sucks" club. &nbsp;You can =
find other members at <a =
href=3D"http://www.miracleas.com/BAARF/BAARF2.html">http://www.miracleas.c=
om/BAARF/BAARF2.html</a> &nbsp;Reasonable read speeds and just terrible =
write ones are expected if that's on your old hardware. &nbsp;Your new =
results are what I would expect from the hardware you've =
described.<br><br>The only thing that looks weird are your ext4 =
"Sequential Output - Block" results. &nbsp;They should be between the =
ext3 and the XFS results, not far lower than either. &nbsp;Normally this =
only comes from using a bad set of mount options. &nbsp;With a =
battery-backed write cache, you'd want to use "nobarrier" for example; =
if you didn't do that, that can crush output =
rates.<br></div></blockquote></div><br><div><br></div><div>I have =
mounted the ext4 system with the nobarrier =
option:</div><div><br></div><div>/dev/sdb1 on /var/lib/pgsql type ext4 =
(rw,noatime,data=3Dwriteback,barrier=3D0,nobh,errors=3Dremount-ro)</div><d=
iv><br></div><div>Yet the results show absolutely a decrease in =
performance in the&nbsp;&nbsp;ext4 "Sequential Output - Block" =
results:</div><div><br></div><div><a =
href=3D"http://malekkoheavyindustry.com/benchmark.html">http://malekkoheav=
yindustry.com/benchmark.html</a></div><div><br></div><div>However, the =
Random seeks is better, even more so than =
XFS...</div><div><br></div><div>Any thoughts as to why this is =
occurring?</div><div><br></div><div>Ogden</div><div><br></div><div><br></d=
iv></body></html>=

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