David T-G said the following on 10/23/2013 11:23 AM:

Well, except that I don't want to waste 100M because of rounding error:-(

You're micromanaging again! 100M on a 1T dive is what, 1%? Most things in life seem to have a rounding error of that order. Try weighing EXACTLY the contents of a bag of chips (crisps to our UK brethren) and see if its within 1% of what's stated on the packet. You're liable to waste more than 1% of your drive in many other ways! -- How long did the whining go on when KDE2 went on KDE3? The only universal constant is change. If a species can not adapt it goes extinct. That's the law of the universe, adapt or die. -- Billie Walsh, May 18 2013 -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org

James Knott said the following on 10/23/2013 02:07 PM:

Anton Aylward wrote:

...

100M on a 1T dive is what, 1%? Actually, it's a whopping 0.01%. ;-)

If I could get that kind of accuracy in life I'd be worried that something was very very wrong. Its bloody unnatural! -- When a subject becomes totally obsolete we make it a required course. -- Peter Drucker -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org

David T-G said the following on 10/23/2013 11:24 AM:

Anton, et al --

...and then Anton Aylward said... % % David T-G said the following on 10/23/2013 06:59 AM: % >If that doesn't work out, I could fall back to partition labeling, % % Back to LVM. % use LVM and that's another problem that goes away.

Fine by me. Now I just need to learn about LVM. Got any good starter pointers? :-)

Oh, and one other question... Do I do my RAID via LVM, or other?

Learn more before you ask that question, as right now its clear a reply yes/no would make no sense. First, LVM can stripe and can do mirroring WITHOUT RAID. Second, putting LVM on top of, say RAID 5 implemented 'normally' can make it more manageable. We've mentioned that in the past - check the archives. But if I were you, I'd take a disk, use parted or whatever to create a good size (300M or so, plenty of headroom!) /boot partition and make the rst of the drive a LVM partition. The install in the LVM partition. Devote say 5G each to /var, /usr/share, /home, /tmp and / Even on a 250G drive(!) that gives tyou lots of free space to play with, but is more than enough to do an install. Then you can start playing around. You can use the LVM tools to add mirroring or striping to the second drive. My point is that you don't have to make all the detailed decisions up front. David, its very clear from this thread that you are massively over-analysing and over-designing the system. Stop micromanaging and Just Do It !

Whether or not to RAID seemed pretty moot these days, so I'm going to try that, but that then leads me to have to decide how to do so if I have some choice. Your idea of creating a fresh volume as needed to replace another was nice, but I don't have that kind of disk space :-) TC

*sigh* My point is that with LVM you can break the obsession that people seem to have before it of over optimizing disk layout. Just make enough to fit now, you can always grow it later ir shrink it if its too much. For a long while I ran my server on the 250G drive referred to above and as I said most of my partitions were 5G - most still are - even with a 60G partition for CD images I found that I usually had more than 50G unused/unallocated to do the kind of file system conversion or space to split a file system that I described. The idea that you have to allocate everything is not only an example of obsessive micromanagement and insistence of getting everything 100% optimized up front, but also allows no flexibility for changes in the future. "Resource Management" needs to be dynamic not constrained by past decisions and locked in place.

The best I could do would be to break the mirror, change one side, transfer the data, and remirror.

*THAT is why I'm suggesting using LVM LVM is not a file system! Its a disk space management system that underlies the file system. -- "Security can be viewed like a construction scenario - build part of a road, and even if and even if you don't complete it, you still have something to drive on; build part of a bridge and you have nothing! Security is like the last." -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org

David T-G said the following on 10/24/2013 07:03 AM:

...and then Anton Aylward said... % % David T-G said the following on 10/23/2013 11:24 AM: % > % >Oh, and one other question... Do I do my RAID via LVM, or other? % % Learn more before you ask that question, as right now its clear a reply % yes/no would make no sense.

Yeah, I know :-(

% First, LVM can stripe and can do mirroring WITHOUT RAID.

Wait a second... What are striping and mirroring except implementation of the Redundant Array of Inexpensive Disks that is the RAID concept?

That's exactly what I mean when I say this isn't a yes/no issue. You're trying to fit things into mental bins without having enough bins/categories and without adequate 'filters' on each bin to say 'no, that doesn't belong here'. RAID is a collection of techniques that may or may not make use of a number of drives in any one of a number of various ways. It helps to know a bit of coding theory and understand Hamming, and also understand what error rates really are and mean, and how different handlers deal with errors. For example, even in ancient history each sector on a DASD had a CRC checksum. CRC - thank you Hamming - allowed the detection AND CORRECTION or errors in the read of the sector, Or in the read of the CRC. To a point. But Back Then, the controllers didn't make use of it, so I wrote a handler for PDP-11 UNIX V6/V7 that did for NorTel. If the errors persisted - that is they weren't statistical fluctuations - I wrote the corrected/best-effort sector to a reserved area and set up a look-aside table entry. Fast Forward and we now have the concept embedded in the controller strapped on every drive you buy. So the effective error rate is way lower than the error rate or the platter media. Engineering is like that - engineers find ways round physical limits. Just watch us defeat the light-speed barrier :-) So RAID-5 made sense of using Hamming checks to correct even those errors. Now go read the articles on why RAID-5 makes no sense with large capacity drives. That's RAID-5 Mirroring? We had mirroring long before the term RAID came into use, back when DASD was still expensive. Heck, I know businesses that mirror their whole site, not just a disk! "Hot Backup". Striping isn't new either. IIR correctly it was even done before DASD was available, done with tape drives. I've never seen that but I've read of it. Yes, once people used computers without disk drives! And yes, they pioneered most of the techniques we use today. With primitive hardware, slow CPUs and a lot less memory. We've quite a few Greybeards on this list. And some of even read about History.

% % Second, putting LVM on top of, say RAID 5 implemented 'normally' can % make it more manageable. We've mentioned that in the past - check the % archives.

Yeah, but the most I'll have is mirrored; I don't have the devices for checksumming. I hate that it's only 50% efficiency, but it's what's available.

More to the point its simple in concept and simple to implement and simple to do recovery. You don't need RAID software - LVM can do it, and if you don't want it done at the OS level there are hardware cards that can do it for you that are pretty cheap. One large AIX multiprocessor system I worked on had, for each (multicore) processor, a (comparative) small mirrored disk pair for just the OS. The data was in the next room, wall-to-wall racks of RAID.

% % But if I were you, I'd take a disk, use parted or whatever to create a ... % but is more than enough to do an install.

That sounds lovely, but it's completely orthogonal to what I want. All of the spinning space is for data and has nothing to do with the OS, which is on a uSD USB drive.

So? You spinning stuff lives under /data and its on drives that implement techniques for speed and reliability - which can be done with LVM. LVM is about resource management. Add another drive - any size, when budget permits or when you find one in the Closet of Anxieties, add it to the volume group, and LVM will make use of it. One drive turns flaky? Tell LVM to remove it from the volume group then pull it. -- The deepest sin against the human mind is to believe things without evidence. Thomas H. Huxley -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org

Greg Freemyer wrote:

On Thu, Oct 24, 2013 at 7:49 AM, Anton Aylward wrote:

...

IIR correctly it was even done before DASD was available, done with tape drives. I've never seen that but I've read of it.

The term is RAIT. I've never seen it either, but knowledge of the term was on a certification test many years ago.

Seem to be described here: http://www.ultera.com/WhatsRaid.htm 10-12 years ago, I worked for the world's largest (by market penetration) manufacturer of tape-drives and -libraries - can't say I've ever heard the term before. -- Per Jessen, Zürich (10.8°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org

Dave Howorth wrote:

Greg Freemyer wrote:

...

The term is RAIT. I've never seen it either, but knowledge of the term was on a certification test many years ago.

Fascinating. I've never heard the term before so I went googling. Apparently, it can produce some stunning performance figures:

"Data General is selling the CLARiiON Tape Array Subsystem comprising between five and seven 4mm DAT tape drives. Data can be recorded in RAID-like striping redundancy, mirrored, or in conventional DAT layout. This unit can provide up to 30GB of unattended contiguous storage. The tape drives can record at sustained rates of 183 - 732 KB/second each but customers should expect sustained backup at around 1 megabyte/second of compressed data after accounting for host overheads."

Cheers, Dave

Did you leave out a smiley? -- Per Jessen, Zürich (14.6°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org

Dave, et al -- ...and then Dave Howorth said... % % Greg Freemyer wrote: % % Fascinating. I've never heard the term before so I went googling. % Apparently, it can produce some stunning performance figures: % % "Data General is selling the CLARiiON Tape Array Subsystem comprising Ah, the Clariions, with their funny spelling... ... % tape drives can record at sustained rates of 183 - 732 KB/second each % but customers should expect sustained backup at around 1 megabyte/second % of compressed data after accounting for host overheads." Whoa! That's like EIGHT megabits! Now we're talkin'... % % Cheers, Dave HANW :-D -- David T-G See http://justpickone.org/davidtg/email/ See http://justpickone.org/davidtg/tofu.txt

Greg Freemyer wrote:

Here's a newer reference (from 2011) to RAIT:

"Why RAIT for BW at NCSA?"

BW => Blue Waters => National Petascale Computing Facility

http://storageconference.org/2011/Presentations/MSST/12.Butler.pdf

Notice slide 9:

Why RAIT at NCSA •  Tape is still viable solution: •  At the scale that we are at (500PB in 5 years) •  To date no reliable, scalable disk solution that has a cheaper TOC •  TOC is total cost of ownership •  Power & cooling required •  Floor Space required •  Length of time for use/viable solution •  Rolling forward for use of 10 years? •  Tape is still the name of the game •  2TB archive site – 20 years ago is a different story

Tape has many attributes that make it a viable solution to many problems.

If a single tape holds 2TB, then they will need 250,000 tapes to hold the full archive! That's a pretty massive tape library. Maybe Per has seen something even close to that. The biggest I have seen are less than 1000 tapes.

I do know of a large Swiss customer that in 1999 bought 40 Powderhorn tape libraries. These hold 6000 cartridges each, so close to 250,000. Tape-drives: an STK T10000D puts 8.5Tb on a tape at 250MB/sec: http://www.oracle.com/us/corporate/press/2008766 -- Per Jessen, Zürich (14.4°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org

Andrey, et al -- ...and then Andrey Borzenkov said... % % ? Wed, 23 Oct 2013 06:59:52 -0400 % David T-G ?????: % ... % > that one is easy :-) How do I find the end of the disk more closely than % > 4TB or 4000GB, though, so that I use it all, other than perhaps by trial % > and error? % % From help mkpart in parted: % % --><-- % Negative values % count from the end of the disk. For example, -1s specifies exactly the % last sector. % --><-- Hallelujah! Yes, that looks perfect :-) Thanks & HAND :-D -- David T-G See http://justpickone.org/davidtg/email/ See http://justpickone.org/davidtg/tofu.txt