[mythtv-users] Fastest RAID for HD?

[Gerald Brandt]

my system is an AMD 64 X2 3800+ with 2 GB RAM. 

I have 5 250 GB HDD in a software RAID5. 3 are on the local IDE control (yes, 2 drives share an IDE bus), and two are on an older Promise Controller. This is what I get for speeds: 

mythbackend raid5 # dd if=/dev/zero of=testfile bs=1M count=16384 
16384+0 records in 
16384+0 records out 
17179869184 bytes (17 GB) copied, 859.12 s, 20.0 MB/s 
mythbackend raid5 # 

Granted, the system is running a few virtual systems as well, but none of them hits the hard drive too hard. 

Gerald 

----- Original Message ----- 
From: "Markus Schulz" <msc at antzsystem.de> 
To: mythtv-users at mythtv.org 
Sent: Saturday, February 16, 2008 9:38:33 AM (GMT-0600) America/Chicago 
Subject: Re: [mythtv-users] Fastest RAID for HD? 

Am Samstag, 16. Februar 2008 schrieb Roger Heflin: 
> Markus Schulz wrote: 
> > Am Freitag, 15. Februar 2008 schrieb Marc: 
> > [...] 
> > 
> >> Don't assume people on this list are experts. Some are, some are 
> >> informed users who have done research, some just make assumptions 
> >> based off of one post or one article they read. 
> >> 
> >> >From a statistical standpoint.. 
> >> 
> >> Raid0 would be the fastest, it is common sense. Your speed for any 
> >> action would be dependent on the number of drives you had or N. 
> >> However if one drive fails you lose all data. 
> >> 
> >> Raid3 or 5 would be the second fastest and would be safer due to 
> >> the ability to continue working without loss of data if you had a 
> >> single drive fail. The difference between these 2 raid types is 
> >> the way they setup parity. Raid3 has a dedicated parity drive. 
> >> Raid5 spreads parity across all the drives. 
> >> Speed of any action on either of these raid configs would be the 
> >> number of drives you had minus 1 or N-1. 
> > 
> > sorry but thats not true. Show me a raid5 with 5-6 drives which 
> > will got 
> > 
> >> 300MB/s _write_ performance... 
> > 
> > Fastest Raid _WITH_ redundancy was raid10. 
> 
> The high dollar hardware raid controllers will get close to the N-1 
> rate, I have benchmarked them under sustained load, but the hardware 
> raid are in the $500-$1000 range, and raid10 with 6 disks will in a 
> perfect world be 180-210mb/second (3 effective 
> drives-60-70mb/second/drive). 

i've built a system two weeks ago with: 

6 * 73Gb 15k 2.5" sas in a smart array p400 (512MB cache) for a HP dl380 
G5 system 

d1:/mnt/disk2# dd if=/dev/zero of=testfile bs=1M count=16384 
16384+0 Datensätze ein 
16384+0 Datensätze aus 
17179869184 Bytes (17 GB) kopiert, 55,6692 Sekunden, 309 MB/s 

d1:/mnt/disk2# dd if=testfile of=/dev/null bs=1M 
16384+0 Datensätze ein 
16384+0 Datensätze aus 
17179869184 Bytes (17 GB) kopiert, 56,1641 Sekunden, 306 MB/s 

-- 
Markus Schulz 


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