Re: [LUG] OT:To Raid or Not Raid (That is the Question)

[Rob Beard <rob@xxxxxxxxxxxxx>]

Gordon Henderson wrote:
> On Thu, 27 Nov 2008, Gordon Henderson wrote:
> 
>> My newest box is nearing completion, I'll post some crude benchmarks
>> soon...
> 
> OK. Here they are.
> 
> The 'server' is an Intel Atom mobo, Dual core HT processor @ 1.6GHz. 1GB 
> of system RAM (533MHz) and I have 2 250GB WDC SATA drives fitted.
> 
> First using hdparm (I did say crude, didn't I?)
> 
> /dev/sda1:
>   Timing cached reads:   1170 MB in  2.00 seconds = 584.88 MB/sec
>   Timing buffered disk reads:  250 MB in  2.65 seconds =  94.47 MB/sec
> 
> /dev/sda6:
>   Timing cached reads:   1172 MB in  2.00 seconds = 586.18 MB/sec
>   Timing buffered disk reads:  244 MB in  3.02 seconds =  80.82 MB/sec
> 
> The first line here is the 'raw' system speed - speed over the bus, etc. 
> Nothing to & from the actual disk.
> 
> The 2nd line is raw head bandwidth. 94.47Mb/sec on sda1 and 80.82Mb/sec on 
> sda6 - sda1 is right at the start of the disk, sda6 starts halfway. This 
> reflects modern disks variable read speed as the sectors per track change.
> 
> (Still - Ye gods, this is the fastest I've seen for a while on a single 
> drive!)
> 
> Working with sda6 - so it's about in the mid-range of the disk:
> 
> 
> ext3 and run bonnie:
> 
>    bonnie -f -u0 -g0 -n0 -s2048
> 
> Version 1.03d       ------Sequential Output------ --Sequential Input- --Random-
>                      -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
> new-siren        2G           69884  39 36717  17           78274  19 260.6   0
> 
> So stream writes at 70MB/sec and stream reads and 78MB/sec.
> 
> 
> Create a RAID-1 out of it:
> 
>     mdadm --create /dev/md0 -l1 -n2 /dev/sd{a,b}6
> 
> hdparm:
> 
> /dev/md0:
>   Timing buffered disk reads:  242 MB in  3.00 seconds =  80.57 MB/sec
> 
> ext3 and run bonnie:
> 
> Version 1.03d       ------Sequential Output------ --Sequential Input- --Random-
>                      -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
> new-siren        2G           66471  40 37136  21           79356  18 436.3   1
> 
> Stream writes at 66MB/sec, reads at 80MB/sec.
> 
> So really - RAID-1 and a single drive really do come out about the same, 
> give or take.
> 
> 
> 
> Re-create it RAID-0:
> 
>    mdadm --create /dev/md0 -l0 -n2 /dev/sd{a,b}6
> 
> hdparm:
> 
> /dev/md0:
>   Timing buffered disk reads:  486 MB in  3.01 seconds = 161.73 MB/sec
> 
> Hurrah! Double the speed :)
> 
> And that could saturate a Gb network interface too.
> 
> ext3 and run bonnie:
> 
> Version 1.03d       ------Sequential Output------ --Sequential Input- --Random-
>                      -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
> new-siren        2G           140446  83 52267  24           162876  36 388.7   1
> 
> So it's stream writing at 140MB/sec and reading at 162MB/sec.
> 
> So if you want speed, RAID-0 is the way to go...
> 
> (But personally, for the OPs requirements to stream a few files, I'd just 
> stick a single drive in it to save the hassle and complexity - especially 
> if the data is already stored elsewhere)
> 
> 
> Oh, and power consumption is 47 watts.
> 
> I'm starting to really like these atom motherboards...
> 
> Gordon
> 

I'm sold on those Atom's now.  Sods law I've just been given a P4 2.4GHz 
CPU and memory and a Celeron D 3.33GHz CPU too.  Shame they're so high 
powered.  Oh well, time to upgrade the kids PC I think.

Rob


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