On Thu, Mar 1, 2018 at 8:39 AM, Wols Lists <antlists@youngman.org.uk> wrote:
On 01/03/18 12:20, Greg Freemyer wrote:
This algorithm was really conceived for arrays with about 100 disks!
I don't think I'm going there anytime soon!
But, it's not totally crazy to buy this 48-slot chassis and fill it up with 2TB drives.
http://www.chenbro.com/en-global/products/RackmountChassis/4U_Chassis/NR4070...
Does it work on a 240V supply? :-)
It's a modular design, so I'm sure you can order it as desired. It can hold 4 PSUs, so 2 hot / 1 spare, Or 3 hot / 1 spare.
2TB drives for $60 are somewhat common, so for about $5K you would have a fairly large spindle count array for testing your code.
That would be brilliant if I could afford it. I don't know as it would be much use to me at home though ...
What capacity LV would that make with your raid 61 variant?
Okay, that's 48TB for a logical raid-6. That gives me 6 logical 8TB drives (or 8 x 6TB) so I could create a 32 or 36TB array. Doesn't sound a lot for 96TB of actual disk, but a mirror would be 48TB so I'm losing maybe 12TB (25%) for parity data - not bad.
That's actually not bad at all for what you're doing. I must have mis-understood earlier comments.
Does your variant require all drives be the same size? If not, does the code support reshapping to let the LV slowly grow over time. Ie, start with 48 x 2TB drives, then replace some with 4TB to grow the LV while maintaining the data? If the code were stable, I might consider doing that in the future.
I don't think raid-10 needs all the drives to be the same size, and this code will probably piggy-back on that code.
That said, mixing different size drives is likely to cause the algorithm to go loopy ... and if your logical array is eight drives, you'd probably need to replace 8 drives at a time for any semblance of safety.
That's acceptable for lots of use cases, probably including mine. (Note I currently have 2 different needs for a storage sub-system. One is for an extremely fast database back-end that will get pounded 24-hours a day. One is for a lightly used archive server. I've used a Drobo in the past for an archive server, and as slow as it is, it worked fine.)
If you wanted sub-1TB drives to test with, these guys sell used drives, but you would need to call them: They have inventory in Atlanta and Las Vegas. I bought a bunch (qty 50?) of 40GB drives from them about 8 years ago. They won't have drives that small now, of course.
https://www.usmicrocorpretail.com/
fyi: I used to audit their disk wiping process for used drives. Every drive gets a 3-pass wipe minimum before it is resold. They have thousands of used (and wiped) drives in inventory. I don't think they sell low volumes (1 or 2 at a time), but I think they would sell 48 in a whack.
I think trans-atlantic shipping would bump the price up :-)
I assume similar exist in Europe. Their real business is data destruction. They go into facilities with lots of confidential data and wipe the computers before anything leaves the building. They typically do that in exchange for them getting the computers for free. The make their income by selling the refurbished used machines. INOP drives get run through chipper/shredder.
I used to wipe friends' drives by shoving them in one of my systems, converting from fat/ntfs to ext, and hammering the drive.
At work years ago, we just used a slack dvd and "dd if=/dev/zero of=/dev/sda", except my colleagues didn't bother to let it run. Maybe 1/2hr and kill it, but that would have done a reasonable job of trashing it - especially for someone who doesn't really know how to try and recover anything.
Nothing wrong with using dd for that, but you do have to let it run. Some filesystems start writing data 1/3rd of the way in and grow towards the front and back ends. A 30-minute wipe may not even get to the real data. I had one matter where a Windows NTFS system was "overwritten" with a Linux system. I was able to recover the full Windows system and testify as to what it contained. FYI: the Linux System was installed, but barely used. My impression is they were trying to destroy the data on the NTFS filesystem, but they failed.
But thanks for the info - I might try and get some kind corp to donate me one of those to play with :-)
Good Luck on that! Seriously, it seems like a reasonable trade. Someone provides you $5K or so of equipment, and you provide the world with your Raid 61 software.
Cheers, Wol
Greg -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org