[mythtv-users] Replace backend 3.5 system disk with 2 2.5 raid1?

[Joseph Fry]

On Fri, Sep 26, 2014 at 10:27 AM, Joseph Fry <joe at thefrys.com> wrote:

>
>
> On Fri, Sep 26, 2014 at 10:08 AM, Mike Perkins <
> mikep at randomtraveller.org.uk> wrote:
>
>> On 26/09/14 14:09, Eric Sharkey wrote:
>>
>>> On Fri, Sep 26, 2014 at 5:13 AM, Simon Hobson <linux at thehobsons.co.uk>
>>> wrote:
>>>
>>>  It means that *every* write to the system filesystem has to contend
>>>> with accesses to all the recording filesystems
>>>>
>>>
>>> The OS drive usage is dominated by reads.
>>>
>>>  Er, no. Every time that a recording is written to one of the storage
>> directories a write is also issued to the database to update the seek table
>> for that recording.
>>
>> That is why it is recommended that the mysql database is not placed on
>> the same spindle as any storage directory, because you're automatically
>> doubling the head movements - at least.
>>
>> You're right in that the OS may mostly be reads but there is always the
>> database IO to consider. That is usually kept on the same drive as the OS.
>
>
> Your suggesting that every time you write to the database, the drive stops
> what its doing, seeks to the proper location, writes the data, seeks back,
> and continues where it left off.
>
> In reality, both the drive itself, and mysql cache the writes... and while
> using a recording spindle definitely causes more head movement it's not
> nearly as bad as your simple model suggests.
>
> Certainly on a heavy loaded system, it is optimal to put the DB on its own
> spindle(s)... but I can tell you from years of experience, on a moderate, 5
> tuner (+9 virtual tuners) mythtv system, this is completely unnecessary.  A
> simple mythtv system with several recordings, OS, and database all on the
> same spindle; I have built several such systems for friends and family.
> There is no reason that 3 hard drives, with a 60GB mirrored partition on
> each for the OS/DB, can't just as easily do the same, considering that
> until I exceed 3 concurrent recordings its typically only writing one
> recording to each drive anyway.
>


Should read what I wrote before hitting send...  the last paragraph should
have said:

Certainly on a heavy loaded system, it is optimal to put the DB on its own
spindle(s)... but I can tell you from years of experience, on a moderate, 5
tuner (+9 virtual tuners) mythtv system, this is completely unnecessary.  A
simple mythtv system works great with several concurrent recordings, OS,
and database all on the same spindle; I have built several such systems for
friends and family.  There is no reason that 3 hard drives, with a 60GB
mirrored partition on each for the OS/DB, can't just as easily do the same,
considering that until I exceed 3 concurrent recordings its typically only
writing one recording to each drive anyway.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.mythtv.org/pipermail/mythtv-users/attachments/20140926/82f5ffd3/attachment.html>