[mythtv-users] HELP! I want my mythtv!

[Hika van den Hoven]

Hoi Simon,

Monday, April 14, 2014, 9:07:23 AM, you wrote:

> 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.

Of cause there is an overhead and I wasn't thinking of database
access. But what is the bandwidth of a modern sata system? Viewing a
recording runs over a 100 Mb network and in optimal situation even
over Wifi. So you can calculate how many simultaneous data streams add
up to the sata bandwidth. Of cause again with administrative overhead
added and writing of cause takes up more bandwidth anytime.
So wat do you need to run into bandwidth problems? I haven't
encountered them with triple write and 1 read, with the database on
the same physical array ( I only have 2 disks in there) also am I
running lvm2 on top of raid1 and is the mythbackend also my all
purpose network server (samba, cups, ldap, named, dhcp, mail, etc.)

So what are we talking of, with present available speed and bandwidth.
I guess you live ten years in the past.

Tot mails,
  Hika                            mailto:hikavdh at gmail.com

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