[CentOS] 40TB File System Recommendations
Rudi Ahlers
Rudi at SoftDux.com
Fri Apr 15 13:17:36 UTC 2011
On Fri, Apr 15, 2011 at 3:05 PM, Christopher Chan <
christopher.chan at bradbury.edu.hk> wrote:
> On Friday, April 15, 2011 07:24 PM, Benjamin Franz wrote:
> > On 04/14/2011 09:00 PM, Christopher Chan wrote:
> >>
> >> Wanna try that again with 64MB of cache only and tell us whether there
> >> is a difference in performance?
> >>
> >> There is a reason why 3ware 85xx cards were complete rubbish when used
> >> for raid5 and which led to the 95xx/96xx series.
> >> _
> >
> > I don't happen to have any systems I can test with the 1.5TB drives
> > without controller cache right now, but I have a system with some old
> > 500GB drives (which are about half as fast as the 1.5TB drives in
> > individual sustained I/O throughput) attached directly to onboard SATA
> > ports in a 8 x RAID6 with *no* controller cache at all. The machine has
> > 16GB of RAM and bonnie++ therefore used 32GB of data for the test.
> >
> > Version 1.96 ------Sequential Output------ --Sequential Input-
> > --Random-
> > Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
> > --Seeks--
> > Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP
> > /sec %CP
> > pbox3 32160M 389 98 76709 22 91071 26 2209 95 264892 26
> > 590.5 11
> > Latency 24190us 1244ms 1580ms 60411us 69901us
> > 42586us
> > Version 1.96 ------Sequential Create------ --------Random
> > Create--------
> > pbox3 -Create-- --Read--- -Delete-- -Create-- --Read---
> > -Delete--
> > files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
> > /sec %CP
> > 16 10910 31 +++++ +++ +++++ +++ 29293 80 +++++ +++
> > +++++ +++
> > Latency 775us 610us 979us 740us 370us
> > 380us
> >
> > Given that the underlaying drives are effectively something like half as
> > fast as the drives in the other test, the results are quite comparable.
>
> Woohoo, next we will be seeing md raid6 also giving comparable results
> if that is the case. I am not the only person on this list that thinks
> cache is king for raid5/6 on hardware raid boards and the using hardware
> raid + bbu cache for better performance one of the two reasons why we
> don't do md raid5/6.
>
>
> >
> > Cache doesn't make a lot of difference when you quickly write a lot more
> > data than the cache can hold. The limiting factor becomes the slowest
> > component - usually the drives themselves. Cache isn't magic performance
> > pixie dust. It helps in certain use cases and is nearly irrelevant in
> > others.
> >
>
> Yeah, you are right - but cache is primarily to buffer the writes for
> performance. Why else go through the expense of getting bbu cache? So
> what happens when you tweak bonnie a bit?
> _______________________________________________
>
>
As matter of interest, does anyone know how to use an SSD drive for cach
purposes on Linux software RAID drives? ZFS has this feature and it makes a
helluva difference to a storage server's performance.
--
Kind Regards
Rudi Ahlers
SoftDux
Website: http://www.SoftDux.com
Technical Blog: http://Blog.SoftDux.com
Office: 087 805 9573
Cell: 082 554 7532
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