[mythtv-users] Fastest RAID for HD?

[Marc]

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).   RAID10 is
really
on the fasted RAID if you are benchmarking seek times (database), if you are

benchmarking raw sequential read and write rates with a good controller
both are about the same speed with raid5/6 or with raid10, and even raid0
only gives a 10-20% gain over raid5/6.    Raid10 only really wins when one
is doing a lot of seeks as small write seeks are expensive on raid5.

Most software raid has a problem that most of the older MB controllers and
cheaper controller cards really don't have independent channels and
interfere
with each other.   On mine I get 70MB/second with one disk, and then it goes
to 108mb/second with a second dd added and then to 115 with a 3rd, so the
controller is utter crap, but still I can get 40MB/second writes out of it
with raid5 and it is good enough.    With the good controllers that goes
70,140,
210,280 and I have tested good controllers and they do exist, one just has
to
be more careful in finding them, and a lot of the recent MB controllers are
good controllers.
_______________________________________________

I used to have a Raid10 for my video storage, but it filled up too quick.
I decided against switching to Raid0 due to not having any fault tolerance.
I saw Raid3/5 as the best option due to more storage space, like Raid0 but
with FT.
Raid5 became my choice for this as we used it at work with great success. We
have servers with 2 (raid0), 6 (raid5), 16 (2x8 drives in raid5 then
striped), and 24 (3x8 drives in raid5 then striped) drive configurations.
Each system except for the 2 drive server has 2 HDD mirrored for the OS and
the other drives are for media storage.
I drool over what I could do with these in a myth setup hehe.