QNAP: Add another drive to RAID 6?

Yesterday I mentioned that everything was working well in terms of building a 7x2TB configuration while the remaining 2TB of data from an external connection was transferred over to the RAID.

Well, this morning all the copying seemed to have finished overnight which meant it was time to plug the last 2TB drive and expand the size of the RAID.

Funny, I was about to say "RAID array" but that is redundant being as RAID does mean "redundant array of individual disks" so saying it would have been like referring to a "redundant array of individual disks ARRAY". No, duh.

It looks to be there is a terminology difference in the jargon used and its confusing. What makes it more difficult is that there isn't enough specific information about what one has to do if using RAID 5 vs RAID 6. After much head-to-knuckle banging (at the possible data loss in one fell swoop of a misconfigured array), a clue on the Wikipedia definition of RAID 6 helped. So it looks to be that its considered by some "RAID 5 + 2 spare disks". Meaning that I could take the "Add hard drive" under the RAID Management tab even if it says only for RAID 5 and implement it on my RAID 6 - which I did. The results are in the first graphic above as well as some intermittent dual-beeping coming from the TS-809 right now.

Those 2 beeps (per the manual, yes of course I read it) mean any of the following things: HDD volume is filling up (don't think so), HDD is indeed full (nope), HDD is in degraded/failed mode (nah), HDD starts/currently rebuidling (YES!!).

So, right now the RAID is rebuilding as a result of the added disk and also calling the expand module. Its still stuck at 1% but like the initial building where I was letting it multi-task copying from the last 2TB drive in the set, its more probably a result of me copying 69-GB of data at 18 MB/s over the gigabit network to one of the NAS' shared drives.

Time to wait and see and a post-update later ....

Apple Mac OS X:Time Machine

Thanks to the QNAP TS-809 Pro being Linux based, it was snap easy to have it create an iSCSI Target.

For those not quite familiar, iSCSI target provisioning allows a shared folder on your SAN (in this case a NAS) to be created and treated as a virtual storage volume.

Specific Mac instructions for all QNAP devices are here. All of this of course wouldn't be possible without globalSAN's iSCSI initiator which they've provided free.

QNAP: RAID size and 2TB drive support?

Per the press release on March 25, its all good finally after much waiting and forum discussion. :-)
http://www.qnap.com/PressRelease_detail.asp?pr_id=128

"Western Digital Caviar Green 2TB (WD20EADS) SATA hard drive is now supported by the entire TS-109/ 209/ 409/ 509/ 439/ 639/ 809 /809U-RP and the latest TS-119/ 219 Turbo NAS series."

"The maximum capacity can be extended up to a total of 16TB now on a TS-809 or 809U-RP' says Andy Chuo, Product Manager from QNAP."

Also, the latest compatibility list published April 22 has the WD20EADS in the list (and notably without any extra remarks!):

Myself, the server just arrived yesterday and I'm currently waiting impatiently for the RAID 6 rebuild to finish on 7x2TB. Currently simultaneously moving files from the front-USB backup (figured I may as well test it) off the final 2TB drive before I add it into the full RAID set.

At 7x2TB its showing me just below 10TB available ... yeah, RAID 6 means (n-2 disks) with each 2TB showing up only as 1.8TB. I just may decide to make it RAID 5 instead when all is done.

Ubuntu Tricks: Compile, Run or be Executed

There will be instances that you may need to protect your shell script contents from being read, such as for instance if they contained log-in or other account details and you wanted to share the script for automation. I was able to find a simple tool that could do this, shc.

Its not part of the usual distribution, so you'll need to have this installed via the package manager or via the terminal using apt-get:
sudo apt-get install shc

After which, simple call the function using this format: shc -f
Example: shc -f mydownloads.sh

What shc does is translate your script into C, then compile it and make it executable. If we ran the example this will result in two-(2) additional files: source and executable
Example:
-rw-r--r-- 1 me me 354 2009-04-25 13:11 mydownloads.sh
-rwx--x--x 1 me me 10948 2009-04-25 13:11 mydownloads.sh.x
-rw-r--r-- 1 me me 11299 2009-04-25 13:11 mydownloads.sh.x.c

The file mydownloads.sh.x is automatically set as executable. Make sure to test it and compare the results with the original script. In my tests you can even ranema the file to something else more descriptive.

But what if in your changing and sharing the executable bit gets unset? Well, that is simple. Just run chmod.

sudo chmod +x

In the example above you'll see the bit permission change from -rw------- to -rwx--x--x.

RAID 6 and that (write intent) Bitmap

For the semi-uninitiated, what is the importance of RAID 6 over RAID 5 is the question. According to 3ware (apparently one of the leading hardware vendors for RAID) say that "Double-parity RAID, commonly known as RAID 6, safeguards against data loss by allowing up to two consecutive drive failures". The technology brief continues to say that RAID 5 is vulnerable to two-(2) types of error conditions: all data is lost in the unlikely event of a second drive failure during a rebuild; and latent media errors that are undetected media defects in the same case as a disk failure on rebuild. Essentially the conditions are the same in that it generally means you have multiple failures in your array instead of the single spare disk you have allocated. There are also performance hit differences, but essentially it looks to be that RAID 6 has a 10% write penalty advantage while RAID 5 has a 15%.

Another good resource introduction to the pro's and con's comes from an article in 2007 saying that RAID 6 is here and viable given how cheaper storage is today. I would have to agree given that USB thumbdrives can now go as large as 64-GB which used to be about the size of my laptop hard drive in 2003. With SSD drives now as large as 250-GB its now viable to get instant startup gratification.

So what about Write Intent Bitmaps? A related discussion on QNAP has some pointers to other external information, but its all not definitive.

Some poor chap basically got flamed on the QNAP forum for asking. Is this the current state of the world today where the smart-asses attack the green apples? Would the preventive thing to do such as a QNAP Korea forum help? Or is this just lashing out payback in some way when non-English based support forums are your only hope for this smashingly great device that you bought from overseas and you can't speak a spit of that other language? Hmmm ... I digress.

To me, given the result of turning on the Bitmap option has alot to do with RAID 6. Thats an over-simplification but too much reading and my best guess (and hope!) is that between the 4-TB spare total I'm going to have on the TS-809 would be better justified if it were also used to ensure that parity and the speed of any possible crash rebuild/resync with write intent bitmap turned on. Given that 2TB initial loss to RAID 5, it had BETTER be.

Game Gems: Brothers in Arms - Hell's Highway (PS3)

Done.