[CentOS] 40TB File System Recommendations

Fri Apr 15 16:26:32 UTC 2011
Ross Walker <rswwalker at gmail.com>

On Apr 15, 2011, at 9:17 AM, Rudi Ahlers <Rudi at SoftDux.com> wrote:

> 
> 
> 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. 

Put the file system's log device on it.

-Ross

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