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Old 06-20-2005, 02:33 PM   #1 (Print)
netdude
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mfsrestore on 1.6 TB disk?

Hi Tivo hackers,

I finally hooked the 2TB SATA RAID system to the HR10-250.
I have photos, but the system won't let me post links :-(

There are 5x 400GB Seagate disks, 1600GB usable.

Anyway, I have two problems:
Using the weaknees MFS 2.0 with LBA 48 support CD
(weaknees_lba_boot_cd.iso)

"not enough extra space to expand on A drive"
when running the following command:
mfsbackup -f 9999 -so - /dev/hda | mfsrestore -s 127 -xzpi - /dev/hdc

hda is the original 250GB disk, hdc is the RAID array.
The PC's motherboard is definitely pre-LBA48.
As you can see in the screenshots the size is detected fine.

This results in the RAID box being bootable and apparently working fine,
but with the original capacity :-(

Second issue probably related is that all the recordings still appear in the target disk (but don't play).

I could use tips here. When I get the entire thing figured out I will post a
complete howto.

Thanks!
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Old 06-20-2005, 05:25 PM   #2 (Print)
JamieP
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Quote:
Originally Posted by netdude
"not enough extra space to expand on A drive"
when running the following command:
mfsbackup -f 9999 -so - /dev/hda | mfsrestore -s 127 -xzpi - /dev/hdc

Let's see 2^31 * 512 ~= 1TB. I'm guessing that there is code in various places (mfstools and/or tivo code) that uses a signed integer for the number of sectors in MFS (maybe individual partitions/zones, maybe for the whole thing). That could make anything over 1TB a show stopper. If you are lucky, these sizes are stored/used as an unsigned integer, which would allow up to 2 TB.

How many partitions are on your source drive? If you already have 16, that could be a problem too.

There are also well known issues with partition/zone sizes > 274GB. The -r 4 option to mfsadd/mfsrestore helps with that, though it will only allow zones up to 1TB.

You'll probably want to increase swap if you are going to run an MFS that big. Various threads are around about increasing swap beyond 127MB.

Quote:
Second issue probably related is that all the recordings still appear in the target disk (but don't play).
As expected when you use the -f option. If you want to preserve recordings, you should use -Ta. Read Hinsdale.

If you want to make this work, you're probably going to have to get the mfstools source (it is on sourceforge) and debug the issues you run into.
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Old 06-20-2005, 09:39 PM   #3 (Print)
c3
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Quote:
Originally Posted by netdude
There are 5x 400GB Seagate disks


Let me guess -- SV2000?

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Old 06-20-2005, 10:40 PM   #4 (Print)
netdude
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> JamieP wrote:
> Let's see 2^31 * 512 ~= 1TB. I'm guessing that there is code in
> various places (mfstools and/or tivo code) that uses a signed integer
> for the number of sectors in MFS (maybe individual partitions/zones,
> maybe for the whole thing).

Indeed :-(

It does display the correct size (1599999 MB) but a negative number of sectors (-1169969152). The number of sectors is 3124998144 (2^32 -1169969152). Math checks: 3124998144 * 512 / 1000000 = 1599999.

> That could make anything over 1TB a show stopper.

Apparently so. I am leaning towards splitting the array into two volume
sets and make them drives A and B.

> If you are lucky, these sizes are stored/used as an
> unsigned integer, which would allow up to 2 TB.

I was hoping so, but apparently not. In the light of this, even if I could
sucessfully create/extend partitions on a 1+TB disk, I now think that it
would be taking chances and be at the mercy of some obscure piece of
code that would not kill it right away but later.


> How many partitions are on your source drive?

13. It's an unmodified / unhacked original disk.

> If you already have 16, that could be a problem too.

It says hd1 to hd13


> There are also well known issues with partition/zone sizes
> 274GB. The -r 4 option to mfsadd/mfsrestore helps with that,
> though it will only allow zones up to 1TB.

I was hoping though that it would be possible to have this pushed to
2 GB but given what's above the point is moot.
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Old 06-20-2005, 11:51 PM   #5 (Print)
netdude
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Quote:
Originally Posted by c3
Let me guess -- SV2000?


No. The SV2000 is not a true RAID (does not do RAID5, for example).
If you want disk redundancy (a must) with an SV2000, all you can get is a total of 800GB usable (4x 400GB, mirrored). In which case it's a lot cheaper to got with an ArcoIDE Duplidisk3.

Mine is based on the Areca ARC-5010, which has a processor, 64MB of RAM, and an LCD control panel. Configured in RAID5 I have 1600GB usable. And, which will liekly come handy with this supposed Terabyte barrier, as it has two separate ATA channels. The guts are the same as the Firewire Depot eRAID.
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Old 06-21-2005, 09:34 AM   #6 (Print)
JamieP
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Quote:
Originally Posted by netdude
No. The SV2000 is not a true RAID (does not do RAID5, for example).
If you want disk redundancy (a must) with an SV2000, all you can get is a total of 800GB usable (4x 400GB, mirrored). In which case it's a lot cheaper to got with an ArcoIDE Duplidisk3.

Mine is based on the Areca ARC-5010, which has a processor, 64MB of RAM, and an LCD control panel. Configured in RAID5 I have 1600GB usable. And, which will liekly come handy with this supposed Terabyte barrier, as it has two separate ATA channels. The guts are the same as the Firewire Depot eRAID.
Raid-5 is known for poor write performance, because a read-compute crc-write cycle is required for each write. A large write cache on the raid controller can help with that. Be interesting to find out if it can keep up with the bandwidth required for writing multiple HD streams.
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Old 06-21-2005, 04:27 PM   #7 (Print)
netdude
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> JamieP wrote:
> Raid-5 is known for poor write performance, because a
> read-compute crc-write cycle is required for each write.

Although this is true in some situations, it does not matter in this case.
The performance issue with RAID5 is with small, random writes. The
Tivo produces large, mostly sequential writes in which case RAID5 is
typically as fast as RAID10 for writes. When the entire stripe set is in
the write buffer there is actually no need for the read, and the
compute-crc is a no brainer for any recent hardware.

> A large write cache on the raid controller can help with that.

64 MB on the board plus the individual disk caches.


> Be interesting to find out if it can keep up with the
> bandwidth required for writing multiple HD streams.

With the large sequential data pattern used by the Tivo, a RAID5 setup
is far superior than any single disk so I don't see a problem. Keep in
mind, it actually works. My issue is with size due to software limitations,
not with performance.

The disks have individual lights. they barely blink most of the time.
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Old 06-21-2005, 05:48 PM   #8 (Print)
JamieP
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Glad to hear it. I had a bad past experience with raid 5 with a controller that had no write cache. Much worse than single disk performance on even large sequential writes. A write cache that is large enough to allow writes to coalesce makes a big difference.
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Old 06-21-2005, 06:14 PM   #9 (Print)
squiddog
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Jamie-

Are you in the storage industry? Because I am, and you sound like me when you are describing the RAID-5 write penalty.

I just wish I could use NFS on Tivo so I could store movies on my Fibre Channel RAID array in my garage! (grin)

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Old 06-21-2005, 06:35 PM   #10 (Print)
JamieP
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Quote:
Originally Posted by squiddog
Are you in the storage industry? Because I am, and you sound like me when you are describing the RAID-5 write penalty.
Just a user.
Quote:
I just wish I could use NFS on Tivo so I could store movies on my Fibre Channel RAID array in my garage! (grin)
It is possible to compile nfs support into a custom tivo kernel. Doesn't really get you want you want though, since it will be a separate file system, not part of MFS. To add the network storage into MFS you'd need network access to raw partitions, rather than to a file system. Since MFS isn't particularly hot swap friendly, your tivo will be down whenever your network or network disks are down.

Probably more interesting is to run a MRV server on a box that has access to the large fiber channel disk array. Then you could move shows back and forth using the MRV mechanisms. I know a few people have experimented with writing a unix MRV server, but I don't think it is ready for prime time.
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Old 06-22-2005, 02:21 AM   #11 (Print)
squiddog
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Yeah, that would be nice.

I haven't hacked into my DirecTV Tivo except to increase drive size, but now with 6.2 I might give it a whirl.

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Old 06-22-2005, 02:30 AM   #12 (Print)
c3
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Netdude, just curious, do you have any RAID5 read/write performance numbers for that system?

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Old 06-22-2005, 10:07 PM   #13 (Print)
netdude
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Quote:
Originally Posted by JamieP
That could make anything over 1TB a show stopper.


Apparently so.
Some interesting screenshots after splitting the RAID box into
2 logical volumes:

http://home.pacbell.net/arn-py/hdtivo/ss3.jpg
http://home.pacbell.net/arn-py/hdtivo/ss4.jpg
http://home.pacbell.net/arn-py/hdtivo/ss5.jpg

It's running right now, time will tell. Does one know how to beg the guys that
write the Tivo code to fix what is seen in ss5? I hope the code that "deletes when need room" is better than the part that displays the total capacity :-)
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Old 06-22-2005, 10:20 PM   #14 (Print)
c3
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Why are there drive errors in ss3.jpg?

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Old 06-22-2005, 10:36 PM   #15 (Print)
netdude
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Quote:
Originally Posted by c3
Netdude, just curious, do you have any RAID5 read/write performance numbers for that system?


No, I just extrapolated from 20 years experience with RAID systems I use on production servers [more on this specific system below].

To nail the RAID5 slow write issue, I would DEFINITELY NOT use RAID5 on a SQL or Exchange server; on such systems, a RAID10 setup is twice (and probably 2.5 times) as much money than a RAID5 setup, but it's 10 times as fast; no-brainer.

However, with large files, in my experience and unless performance is a top priority regardless of price, the extra cost of a RAID10 system is not justified. You can only watch one and record two; as long as the system can handle it there is no point in spending 2x the money to have it twice as fast.

Now, specifics about the ARC-5010:

- It's my first one; the Tivo is the only hardware I have RAIDed that does not have 64-bit PCI-X slots and drivers for the OS). Although it's not cheap (700 bucks) it does include both the RAID controller, the LCD panel and a 5-bay hot-swap cage. If I had to do the same setup for a PC I would pick a Supermicro cage and an LSILogic 6-channel card for about the same price.

Large capacity fault-tolerant storage does come at a price. Keeping mom's soaps on-line at four nines does have a price but is priceless :-)

- Suprisingly, the Tivo negotiates the speed with the disk at UDMA33 only (the nice thing about having a real RAID setup is that you can actually display the DMA speed negociated on the bus).
Although the speed limit might be a by-product of the double ATA bridging, I am MUCH more concerned by the the throughput of the bus at UDMA33 than by the RAID5 performance. If I do encounter performance issues, my first priority will be to have the Tivo and the RAID card talk at UDMA66 or better.

I have a LED that displays activity on channel 0 (the "A" drive", and I have leds for each individual disk. I can tell you that the free/busy ratio of the channel vs. the disks is that the channel is in use 2 to 3 times as much as the disks are, likely thanks to efficient caching.
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Old 06-22-2005, 10:40 PM   #16 (Print)
netdude
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Quote:
Originally Posted by c3
Why are there drive errors in ss3.jpg?


The ATA commands to query the disk's cache size are obviously not implemented in the RAID firwmare. SMART is not implemented either. This does not bother me, actually. The RAID card knows better than the PC or Tivo how to handle cache and fault tolerance.
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Old 06-22-2005, 11:28 PM   #17 (Print)
JamieP
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Quote:
Originally Posted by netdude
No, I just extrapolated from 20 years experience with RAID systems I use on production servers.
Sorry to put you on the defensive on this. I certainly believe that this device is capable of sustaining the bandwidth required by an HDTivo. I think the write cache is key.

A friendly little jab I just can resist though: The original paper proposing the raid concept (link) was published in 1988. That's 17 years ago. Maybe you should have published your work first :-)

Glad you got it working, BTW.

Last edited by JamieP : 06-22-2005 at 11:46 PM.
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