Film-Tech Forum ARCHIVE: Add Capacity to Dolby DSS200

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Posted by Cameron Andrews (Member # 5246) on 09-13-2011, 02:30 PM:

I have a Dolby DSS200 unit that I would like to increase the storage capacity on. There are 8 content drive bays with only 4 in use. Can I put 4 drives in the empty bays (exact matches to the original 4) and double my capacity? If so, will it automatically recognize the new drive array or will it need to be configured? I don't understand RAID that well, but I would imagine that just adding 2 drives wouldn't be an option as it wouldn't complete the RAID array. Thanks!

Posted by Steve Guttag (Member # 268) on 09-13-2011, 04:13 PM:

Nope...on the DSS200...all you are going to be able to use are the four drive bays. There are those of us that have speculated that the DSS200 or its frame might some day turn into Dolby's LMS...but that is just speculation.

In any event, if you want to increase capacity...you'll need to change all four of the original drives. However, you will need to have an INSTALL disc (not an UPGRADE) of the software version you are running...AND you will need to reconfigure the unit as everything will be wiped...and finally you will need to load ALL of the content back on (including the blanks and such).

Therefore, before you do such a thing...get a CRU drive and back everything you want to keep up onto that so you will have content to reload.

Write down all of the configurations if they are not Dolby's standard (since Dolby's Wizard will walk you through their standard configurations).

The other thing you need to allow for is the time to completely configure/initialize...etc the RAID...This is the sort of thing to do at the END of the day so you have over-night to let it configure. It would be even better to have a "mule" to allow you to get the drives all set, configured, loaded...and then just move the drives over (I've done this with complete success!). However, most don't have a spare player laying around unless you are doing installs.

-Steve

Posted by Cameron Andrews (Member # 5246) on 09-13-2011, 05:21 PM:

That makes sense. Would it also work to replace the drives one at a time and let raid rebuild between each replacement or will the difference in drive capacities cause problems?

Posted by Scott Norwood (Member # 30) on 09-13-2011, 05:40 PM:

Won't work. You can remove a drive and replace it with a larger one, but the RAID will be rebuilt using only the capacity of the original drive. In other words, if you remove a 1TB drive and replace it with a 2TB drive, the RAID will only use 1TB, wasting the additional 1TB. RAID5 only works by using stripes of identical size on each disk, which is why you can't use the additional space. Also, you will degrade the RAID performance by using dissimilar drives.

Note that the Dolby server _will_ boot off of a CD. In principle, you could boot it off of a Knoppix (or similar) CD, back up the contents to an external disk, insert all new drives, rebuild the array, then boot off of the CD again, re-partition, restore from backup, and re-install the boot loader. This is complicated by the fact that the Dolby server uses the XFS filesystem, which not every Linux kernel will support. In short, it can be done, but don't even try unless you have significant experience with Linux. And even then you would want to have an install CD handy.

Posted by Ken Lackner (Member # 1002) on 09-13-2011, 09:38 PM:

quote: Cameron Andrews
Would it also work to replace the drives one at a time and let raid rebuild between each replacement or will the difference in drive capacities cause problems?

quote: Scott Norwood
Won't work. You can remove a drive and replace it with a larger one, but the RAID will be rebuilt using only the capacity of the original drive.

This CAN be done with a Sony. Anyone know if it can be done on a Dolby?

Posted by Steve Guttag (Member # 268) on 09-14-2011, 04:27 AM:

Ken...you could replace the drives one at a time...but as Scott said...at each replacement, you only get what you had before. That is...if it is a 1.5TB system with 500GB drives...if you put a 1TB drive in...it will format and use that new 1TB drive as a 500GB since that is the size of the ARRAY. As you put each drive in, one at a time...you get the same result...after all four drives are in...you still only get the effective space of 1.5GB for the whole array despite now having 3TB worth of drives. Once you reformat (which will wipe the data on those drives) ... you will then get to use all of them to their capacity.

Now it would be nice if there was a means such that once all drives are of a larger capacity that it could self-enlarge but that does not seem to be how it works. Folks with much more RAID knowledge than I would have to explain why.

-Steve

Posted by Monte L Fullmer (Member # 2797) on 09-14-2011, 01:39 PM:

Plus, isn't there many variation of the RAID configuration on how the drives are allocated?

E.G. I know of a LS that has 9, 1tB drives, but the total capacity is about 6.5tB. Thus, which RAID configuration is doing this one?

But true - you add drives to a RAID, you have to had all the drives formatted to be recognized as one drive by the system.

Posted by Frank Cox (Member # 6258) on 09-14-2011, 01:54 PM:

How much data can be stored on a RAID array depends on the amount of redundancy that the scheme includes. Obviously a scheme with more redundancy will be better able to tolerate drive failures and/or corrupt data than a scheme with less redundancy but the trade-off is that you have less space available for your data since the extra data that provides the fault-tolerance has to be stored somewhere, too.

For example, at the extreme end RAID 6 requires a minimum of four drives in the array but can tolerate the failure of two drives so in a 4-drive RAID 6 array you can actually store less than half of the data that the number of drives would otherwise suggest. Other schemes provide differing amounts of usable space vs the size and number of drives provided in the array and it's always a choice or trade-off between safety of your data, available storage capacity and speed of interaction (storage and retrieval) with your data.

Posted by Scott Norwood (Member # 30) on 09-14-2011, 02:27 PM:

What hardware and OS does the Sony unit use? Is the RAID created in hardware or software?

Posted by Monte L Fullmer (Member # 2797) on 09-14-2011, 04:28 PM:

Sony uses Linux OS, and I do believe that they also use Scheme 6 RAID.

Posted by Cameron Andrews (Member # 5246) on 09-15-2011, 12:09 PM:

So if the OS is located on the removable drives, thus having to reload after installing new drives, does that mean that if you pulled all drives from one server and put them in another it would boot? Could you not then run the config and then have a fully functional server with the same content that was on the first server? The only reason I could see to do this is if you had a server failure and had to use a "spare" server (Who has one of those kicking around??). I'm more interested in the theory of operation then actual application here. But hypothetically speaking, could it be done? And if so, is there a way to back up your config file like a DTS XD10 does?

Posted by Monte L Fullmer (Member # 2797) on 09-15-2011, 12:58 PM:

Some servers usually stores the OS in a flash storage section of the unit where it makes the drives fully dedicated storage drives where you can load the drives to full capacity.

Doremi and Sony servers uses flash memory to store the OS.

Not sure with Dolby (and with GDC servers) though if they run the OS from flash, or it's on a partitioned section of one of the drives, but can see DOLBY and GDC also using flash to store the OS to allow the drives to be used in a full storage condition.

If you lose the OS, that is when the tech has to come to do a reinstall of the OS from his laptop.

Posted by Mark Gulbrandsen (Member # 72) on 09-15-2011, 02:41 PM:

Actually I have had booth people restore Dolby Servers in the past. Updating is a little complex on the Dolby compared to others but there is always someone in the booth that is computer savvy enough to follow the instructions. Doremi and GDC wouldn't require a RAID rebuild or content reload on an OS fail.

Mark