[mythtv-users] Fastest RAID for HD?

[Marc]

-----Original Message-----
From: mythtv-users-bounces at mythtv.org
[mailto:mythtv-users-bounces at mythtv.org] On Behalf Of Mark Hutchinson
Sent: Thursday, February 14, 2008 1:07 PM
To: Discussion about mythtv
Subject: Re: [mythtv-users] Fastest RAID for HD?

So just for speed, a RAID 0 ( software raid ) will be fastest then for  
transient recordings?  What about LVM?


On 14-Feb-08, at 10:57 AM, John Drescher wrote:

>> From my experience, with Linux, software raid is a lot better than  
>> hardware
>> raid.
>>
> It depends on tuning. HW raid with a decent sized write cache (turned
> on) will suffer less from thrashing than software raid using the
> default cache sizes. I mentioned turned on, because a lot of cards
> default to turn off the cache unless you have purchased $150
> battery...
>
> John
> _______________________________________________

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.

LVM has no ability to recover from a drive failure and cannot be compared to
a raid0 array for speed.
Raid0 writes data across all disks in the array.
LVM writes data to the first disk in the volume until it reaches the end of
that disk then it continues to write data to the next disk in the volume.