[mythtv-users] HELP! I want my mythtv!
Simon Hobson
linux at thehobsons.co.uk
Mon Apr 14 07:07:23 UTC 2014
Hika van den Hoven <hikavdh at gmail.com> wrote:
>> the array, and reading might not be any faster - it's very
>> application dependent and in some cases the array can be slower than
>> single drives. For Myth, unless you want the redundancy, then raid is not beneficial.
>
> No, it is file size dependant.
I don't want to start a war over this, but is it *APPLICATION* dependent - specifically the file size (application dependent) *AND* how the application accesses that file (application dependent). Yes it is the kernel that manages it, but it is the application that determines the file size and access profile. Myth is very good in that respect in that it generally accesses large files in a linear read (but only if you are watching/accessing one recording file), throw a big database with gigabyte files of small records at it and you may even see performance poorer than single drives.
It's a complicated area which is outside the scope of this list, but lets just leave it at "for MythTV, there isn't generally any advantage of using raided disks *UNLESS* you want the redundancy and are prepared to take the performance hit that it generally involves".
> Actually storage groups only can give speed increase if you're
> recording two shows or watching and recording and they happen to be on
> separate disks. With raid1 the read speed increase is always (if the
> file is big enough).
Correct, but if you aren't in a situation where the benefit of storage groups comes into play, then you also aren't in a position where RAID1 is of any benefit (performance wise).
> In optimum situation the max increase with storage groups can be
> higher, but is not guarantied!
True, but the same applies (more so) to RAID.
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