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 Post subject: New rig questions.
PostPosted: Tue Mar 09, 2010 7:09 pm 
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Joined: Fri Oct 20, 2006 12:04 pm
Posts: 905
Location: LA, CA
Looking to reconfigure my setup and add a MBE that would have no FE duties. HDHR, PVR recordings with a HD-PVR maybe coming down the road.

Questions:
1) Is there benefit to having the database and main storage group(s) (ie /myth/tv) reside on different drives?

2) How stable would a single drive caring for MBE, database, and network FE's (no recordings) be?

3) Should a MBE need more then 1GB ram, GigE network?


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 Post subject: Re: New rig questions.
PostPosted: Tue Mar 09, 2010 9:52 pm 
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Location: Arlington, MA
Too Many Secrets wrote:
1) Is there benefit to having the database and main storage group(s) (ie /myth/tv) reside on different drives

Some for performance, but unless you're serving quite a few FE machines you're not likely to come close enough to the HD bandwidth limit that splitting them makes a difference.

On the reliability count, I'm not sure how the "split the workload" gain for wear and tear balances out against "more things that could fail" loss. (The failure rate for two drives getting equal use is 2x the rate for one, so it would come down to how usage patterns affect the MTBF. At a guess it could decrease overall reliability)

Too Many Secrets wrote:
2) How stable would a single drive caring for MBE, database, and network FE's (no recordings) be?

Quite. Again it would come down to the % of disk bandwidth the FE's demanded.

Too Many Secrets wrote:
3) Should a MBE need more then 1GB ram, GigE network?

I might go 2Gb (dead cheap) just for some extra buffer headroom if you're serving a lot of FEs.


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 Post subject:
PostPosted: Wed Mar 10, 2010 9:02 am 
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Location: Ft. Worth TX
I am kinda conducting an experiment on this very thing. I have two essentially identical IBM 6225s running LinHes (6.01 & 6.02).

The 6.01 machine has a 30 gb scsi drive running the program and a little myth/tv storage. The rest of the storage is on a myth2/tv2 1tb sata drive.
This combination has been running like the sunrise, and has reduced picture pauses to near zero.

The 6.02 machine runs all off a 1 tb drive (I didn't have a small sata available when I built it up...) I am not sure there's any real difference to notice between them.

I've yet to have a drive fail in 30 years (using up all my luck ?...[they get small and obsolete first...]) so I'm not too concerned about half reliability.

I run 2 mb of memory in each, just so I never see 'swap' being used. (The pauses, y'know...)

From my experience so far, I'd have to say 'six of one, half dozen of the other', your choice.

As to gbE, I'd like to know the answer myself. I've gone over to HDhomeruns (2 dual HDHRs) from air-2-PC tunercards. HDHRs are much less fussy about being fed a very strong signal or get blocking and tearing.
I have a 100 wired eithernet and wonder if that will be enough when I have three HDHRs bouncing streams around in it.


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 Post subject:
PostPosted: Wed Mar 10, 2010 11:19 am 
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Location: LA, CA
Thanks for the feedback. Really appreciate the input and experiences.

As for the splitting up of DB and recording storage (1), I have concerns about drive delays/thrashing during multiple simultaneous functions. I often record multiple streams, do com-flaging, and serve media to at least 1 FE all at the same time. Most of the time this is off a single MBE/FE unit (SATA-300 500GB WD drive). I too often experience pauses and stuttering due to disk activity. I also see DB 'corruption' often and run the repair scripts daily via cron.

I personally like the idea of splitting up the main / and swap from the /myth/ and ultimately /myth/tv /myth/video storage. I think however that the DB and /myth/tv would be best residing on different drives in the same case. That said, I'd be glad to find this not the case for simplicity sake alone.


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 Post subject:
PostPosted: Wed Mar 10, 2010 1:12 pm 
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Location: Ft. Worth TX
My two-drive 6225 has been the best performing mythbox that I've built yet.

But it looks like you'll be breaking trail on this one: Your intended useage will flog your box harder than my plain-vanilla useage.

:D


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 Post subject:
PostPosted: Wed Mar 10, 2010 2:47 pm 
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Location: Calgary, Canada
Too Many Secrets wrote:
I personally like the idea of splitting up the main / and swap from the /myth/ and ultimately /myth/tv /myth/video storage. I think however that the DB and /myth/tv would be best residing on different drives in the same case. That said, I'd be glad to find this not the case for simplicity sake alone.

To really maximize performance you could also split off /var onto its own (third) separate drive. Seems to me most casual Linux users don't pay much attention to /var, but I'd bet that it's actually the most-accessed folder on the system in terms of quantity. (Think about it... almost every daemon that logs, which of course many do, is writing there! Plus logging is not all that /var gets used for.)

Obviously you wouldn't want to use a new drive just for this purpose but an older drive of the ~30GB era would be ideal if you've got one lying around.

At the very least, consider making /var its own partition when you redo your setup, for future flexibility. (I did this on mine, it's not hard... basically you just reboot with a rescue disk, backup then move the folder, and edit fstab.)


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 Post subject:
PostPosted: Wed Mar 10, 2010 6:44 pm 
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Location: LA, CA
paulsid wrote:
Too Many Secrets wrote:
I personally like the idea of splitting up the main / and swap from the /myth/ and ultimately /myth/tv /myth/video storage. I think however that the DB and /myth/tv would be best residing on different drives in the same case. That said, I'd be glad to find this not the case for simplicity sake alone.

To really maximize performance you could also split off /var onto its own (third) separate drive. Seems to me most casual Linux users don't pay much attention to /var, but I'd bet that it's actually the most-accessed folder on the system in terms of quantity. (Think about it... almost every daemon that logs, which of course many do, is writing there! Plus logging is not all that /var gets used for.)

Obviously you wouldn't want to use a new drive just for this purpose but an older drive of the ~30GB era would be ideal if you've got one lying around.

At the very least, consider making /var its own partition when you redo your setup, for future flexibility. (I did this on mine, it's not hard... basically you just reboot with a rescue disk, backup then move the folder, and edit fstab.)


Yes, I was wondering about all those log files. I don't think it would be too hard to move, just a symlink should do it (and another drive of course). Thanks for the tip, I guess as long as we're making the 'ideal box' let's go big!


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 Post subject:
PostPosted: Wed Mar 10, 2010 6:53 pm 
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Location: Los Angeles
I'd put /data/var/cache/pacman/pkg/ on it's own partition. If you don't keep an eye on it, it can fill your root partition with old (and new) packages, bringing your box to it's knees. :lol:

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 Post subject:
PostPosted: Thu Mar 11, 2010 9:36 am 
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Joined: Wed Feb 08, 2006 6:13 pm
Posts: 480
Location: IN
Maybe I'm just blissfully ignorant but some of your partitioning schemes seem like overkill when for $90 I just bought a 1TB Samsung Spinpoint F3 drive that can sustain over 100 MB/s:

Code:
hdparm -Tt /dev/sda8

/dev/sda8:
 Timing cached reads:   6102 MB in  2.00 seconds = 3052.76 MB/sec
 Timing buffered disk reads:  418 MB in  3.00 seconds = 139.16 MB/sec


This drive should *in theory* have no problem keeping up with anything GigE can throw at it. Granted I'm using a brand spanking new disk with 500GB platters to achieve this but I'd much rather trust my data to this drive than an eight year old 30GB drive from my Uncle's Nephew's sisters old PC.

Can someone point out a flaw in my logic? Other than reuse of older hardware is there any advantage?

Martian

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 Post subject:
PostPosted: Thu Mar 11, 2010 11:11 am 
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Joined: Thu Apr 03, 2008 11:42 pm
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Location: Calgary, Canada
Drive throughput isn't going to be the bottleneck, it's the number of seeks. If the system is serving content to 3 different FEs and recording 2 shows and writing logs and reading binaries all from the same drive, the accesses add up. Caches and buffers are only so big, so sooner or later the system will have to wait for the platter to seek and read/write data.

I'm not up on what modern drive seek times are but even if it's down to 5ms now that's still an eternity in processor time, and if happens 10 times a second, now you're taking a 5% of your system performance, which is not an insignificant number. With multiple drives, not as many seeks are needed as often so performance can go up. (It's not guaranteed, but probable.)

Now I'm not saying this is necessarily going to be a problem, just that it's a legitimate concern. How big the performance hit is and whether it's actually an issue on a busy MBE or not remains to be seen. On a dual-core MBE-only system in particular, I agree that it probably won't be a problem. Even if it isn't, though, splitting your system over drives doesn't really hurt anything. Plus if drives are so cheap, Why Not Get Two? :)

Martian wrote:
I'd much rather trust my data to this drive than an eight year old 30GB drive from my Uncle's Nephew's sisters old PC.

Yes, but I was only suggesting using an old drive for /var, and there is no valuable data there. So if it fails you restore the directory structure from backup and carry on with your life.


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 Post subject:
PostPosted: Thu Mar 11, 2010 9:48 pm 
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Location: Arlington, MA
Martian - That's pretty much what I was talking about. Unless the drive system is right on the border line of overload, seek contention shouldn't be a performance issue, and multiple drives weren't going to be an improvement in the systems hardware reliability.

My "back of the eyeballs" (like back of the envelope, but less formal ;-)) math showed a bigger improvement for less $ by going with more RAM rather than multiple drives.


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