[mythtv-users] Question re: available SATA ports and linux software RAID

Another Sillyname anothersname at googlemail.com
Sat Apr 9 16:35:11 UTC 2011

On 09/04/2011, digid myth <digidmyth at gmail.com> wrote:
> Here is my take on this.
> My goal was to get the power footprint down on my main server in the house
> which is also my Myth Backend. We have 2 Myth Front Ends, and 2 Crystal
> Cinema Media Players for the Kids rooms. My goal is to run an total average
> of 100 watts on this server. I am not there yet, with numbers running around
> 120-150 watts each month. This is down from 400 watts for the old server.
> For a living I am a system administrator for some large scale systems so am
> very familiar with availability and data recovery.
> Here are a couple of rules that I have for my installation.
> All backups are to other disks, I have discontinued use of tape.
> A data drive or raid set can not share the same power supply as its backup
> drive. I have had a PS go bad and take out all the drives connected in the
> past.
> Backup drives should be kept spun down or left off unless in use.
> Keep the drives as cool as possible, and in standby if possible.
> Drive Access speed only needs to be slightly faster than the max network
> transfer rate.
>     (I am very happy with the 2TB Samsung Spinpoint F4 drives)
> No drive will have active data on it until it has been on line and running
> for 4 weeks.
> All drives are replaced every 3 years, old drives may be used for
> offline/offsite backup storage.
> The more drives in a raid array the more likely you are to have a failure,
> so if you do not need high availability, I try to stay away from it on this
> setup.
> Video archives do not change much and are not high availability so they do
> not live on a raid.
> Backup Everything that is important or takes a long to to recover.
> My main server is a dual core AMD with 6 Gig of ram. Video source is a HD
> Homerun on an antenna.
> It runs the Myth Backend, Zone Minder Security System, with 4 cameras, Anti
> Spam for all our mail accounts, A OSX VM that keeps the family's calendars
> and music in sync, and occasionally transmission and handbrake. I am on the
> edge of using all the resources of this server at times, but it is not
> uncommon for it to be sending 3 streams out, and recording 2 channels at the
> same time, and ripping a DVD and everythings works fine.
> Attached to the server is a rosewell RSV-8 storage tower that holds 8
> drives. I purchased from NewEgg
> http://www.newegg.com/Product/Product.aspx?Item=N82E16816132016&cm_re=rosewell_sata-_-16-132-016-_-Product
> This tower supports 8 drives on 2 sata channels and uses sata port
> multiplication, which means that is shares the bandwidth of 4 drives with
> the bandwidth of 1 sata channel. This has not proven to be a problem in my
> setup.  It comes with a 2 channel PCIe ESATA card, and cables. I had
> problems with the cables and replaced them with more flexible higher quality
> ones, and have not had any more problems with the drives going off line.
> In the main dual core server.
>   2 DVDROM Drives
>   2 320G sata boot drives in raid 1 (These are very fast seagate drives)
>   2 2TB sata drives in raid 1
>   1 2TB sata drives that we use for our OTA recordings from myth
>   2 2TB sata drives in raid 1 that we use for general data storage
>   In the 8 bay tower
>   2 2TB sata drives for backups from the laptops and workstation on the
> network
>   2 2TB sata drives that hold our general movie collection set up to myth as
> storage groups.
>   2 2TB sata drives that are spares / general purpose drives.
>   I have 2 bays open for future expansion.
>   I have a 2nd server that was built for speed and on demand uses. It has a
> 4 bay sata enclosure that holds drives for backups from the main server.
> http://www.newegg.com/Product/Product.aspx?Item=N82E16816132029&cm_re=rosewell_sata-_-16-132-029-_-Product
> It holds
>  2 2TB drives to backup the movie collection to.
>  1 2TB drive to backup the data raid to
>  1 1TB drive to hold the main server backups.
>   This server is normally powered down.  This server is up only when I need
> its resources. I use it to run VM's and to rip DVD's etc. The drives are
> only up when backups are run. (Just a note this servers power is not in my
> measurements that I mentioned above, as it is an on-demand server, and was
> build for speed and not power savings)
>   The one hole in my system is that the OTA recording are not backed up or
> raided at this time. My next plan is to move this to a raid, but it will
> still not be back backed up. The myth database lives on the main raid and is
> backed up to the data raid. Storage groups join the main movie drives, so
> the size of the drives does not matter, therefore it does not need to be
> raided, and I can add drives as needed with out having to reconfigure the
> filesystems etc.  As one drive fills up it changes very little, so backups
> for full drives are uncommon. On the drive we are adding movies to, I do a
> manual backup to the 2nd server when I add movies to it. All other backups
> are automated, and I use custom software that I wrote that works very much
> to Apples Time Machine, using rsync. Laptops and workstations are backed up
> every day, the server drives are backed up every week, or before and after I
> make massive changes. This makes backups very quick and painless as only
> changed data is backed up. Data that has not changed is simply linked to the
> file in the previous backup.
> To help save on drive wear and tear I turn off the recording of access times
> (noatime in the fstab file) to off on all drives but the OS drives, and the
> Myth OTA recording drive.
>  All drives are put in sleep mode after they have been idle for 30 min. This
> works well on the software raid1 but I have had problems doing this with
> software raid5 and raid6. If you are monitoring the drives using the SMART
> utilities there is a flag you can set to check to see if the drives are
> asleep and it will skip them. Otherwise SMART will wake the drive up, or
> never let it go to sleep.
> Remember you have to take the whole system into account, and one big raid in
> my opinion is definitely not the way to go with myth. The developers have
> given us storage groups for a reason. The advantage of storage groups is
> that adding disk space only requires you to add the drive, no changes need
> to be made to your existing data, which is always safer. Only the active
> drive needs to be awake and running when you are recording, or streaming a
> movie, This reduces the overall time on the drive, and reduces the heat that
> is generated. Heat is the number one killer of hard drives. If you loose a
> drive you only loose the data on that drive, not a whole array. I have seen
> many raid5 and raid6 arrays fail either through hardware or software. If
> your controller goes bad the whole array is lost in some cases.  It is not
> uncommon for  someone make a mistake rebuilding a failed array and wipe the
> whole array out. Never rely on RAID as your backup. With 2TB drives commonly
> sold for $75.00 at newegg the price of the backup drive is peanuts. Your
> backup plan also needs to include some time of offsite backup for you most
> critical data. My 2TB raid on the main server is copied out to and external
> 2TB drives and taken off site at least twice a year. I have 2 drive I rotate
> out off site for this. Digital Photo's, personal data etc are kept on this
> raid so everything that is really important is off site incase of fire,
> flood, theft etc.
> This setup has worked good, and has evolved over the years into what it is
> today. Getting the power down is more of a hobby than a necessity. About the
> only way I am going to be able to get the average any lower is to eliminate
> the external drive tower and put all the drives in the case, with a high
> efficiency power supply. I am considering it, but the external case sure is
> nice, and I am not sure that it is worth the 20 watts for so that I could
> save. Remember that the biggest way to improve the reliability of your
> system to to eliminate as much heat as possible. If you can keep the
> server(s) in a basement, and keep everything cool you will get good service
> from your system.
> I hope this will give you some ideas, and also help those that are building
> or evolving their MythTV servers.
> Dale

To anyone serious about keeping their drives cool and therefore less
prone to failure I'd recommend they look at this "Mobile Rack"


Holds 5 drives in 2 x 5.25" bays, with built in fans and supports hot
swapping (subject to your SATA card supporting it).

Even in the very hot summers we had a few years back in the UK when
ambient temps were in the mid 30's C my drives never got above low
40's C, most of the time the drives are in the 32-38 C range.

I'm sure there are other one's out there just as good but I've had
these for over 8 years and never a problem (fingers crossed).

They're available in Black as well which is a much better colour IMHO.

Hope it is useful to someone.

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