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

[Gordon Henderson <gordon+dcglug@xxxxxxxxxx>]

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

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