Linked by Thom Holwerda on Mon 18th Jan 2010 16:57 UTC, submitted by wanker90210
Hardware, Embedded Systems ACM's latest journal had an interesting article about RAID which suggested it might be time for triple parity raid. "How much longer will current RAID techniques persevere? The RAID levels were codified in the late 1980s; double-parity RAID, known as RAID-6, is the current standard for high-availability, space-efficient storage. The incredible growth of hard-drive capacities, however, could impose serious limitations on the reliability even of RAID-6 systems. Recent trends in hard drives show that triple-parity RAID must soon become pervasive."
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RE[3]: RAID Z
by gilboa on Tue 19th Jan 2010 14:37 UTC in reply to "RE[2]: RAID Z"
gilboa
Member since:
2005-07-06

I'm not quick to dismiss ZFS.
I actually have a OpenSolaris VM w/ZFS on this machine (under Linux/KVM).

I am saying that ZFS is not the solution to everything.
It cannot replace hardware RAID controllers.
Some people (like me) have major misgivings about the lack of separation between the disk level (E.g. Hardware / Software RAID) and FS layer. (E.g. NTFS, ext4, etc).
And last and not least, *Solaris is also an OS. And you don't select an OS just because it has a shiny file system.

- Gilboa

Edited 2010-01-19 14:46 UTC

Reply Parent Score: 2

RE[4]: RAID Z
by computeruser on Tue 19th Jan 2010 15:18 in reply to "RE[3]: RAID Z"
computeruser Member since:
2009-07-21

It cannot replace hardware RAID controllers.

For some applications, ZFS can be a better (cheaper) fit than hardware RAID.

Some people (like me) have major misgivings about the lack of separation between the disk level (E.g. Hardware / Software RAID) and FS layer. (E.g. NTFS, ext4, etc).

If you don't like it, then why don't you explain why you think it is a bad idea instead of trolling?

And last and not least, *Solaris is also an OS. And you don't select an OS just because it has a shiny file system.

No one said "Everyone should use Solaris because it has ZFS". The first post mentioning ZFS simply mentioned that ZFS now has triple parity in OpenSolaris.

Reply Parent Score: 1

RE[5]: RAID Z
by gilboa on Tue 19th Jan 2010 17:35 in reply to "RE[4]: RAID Z"
gilboa Member since:
2005-07-06

A. I wasn't trolling. I have nothing against ZFS or OpenSolaris (I use them both... not in production, though). I am -very- much against the people who automatically post "use ZFS instead" message as a response to each and every storage-related-news-piece.

B. As for your question, I see ZFS' lack of layer separation as major issue due to the following problems:

1. We have >30 years of experience with dealing with FS and volume manager errors. In essence, even if your FS completely screwed up huge chunks of its tables (no matter how many copies of said tables the FS stores), in most cases the data is still salvageable.

2. We have >20 years of experience in getting screwed by RAID errors. If something goes wrong at the array level and you somehow lose the array data/parity mapping or parts of it, the data is doomed. Period.

3. As such, I'm less afraid of trying new FS's, ext3, ext4, btrfs, ZFS. As long as I can access the on-disk data when everything goes to hell, I'm willing to take the chance. (Of-cause, as long as I don't get silent corruption that goes undetected for years...)

4. On the other hand, I want my RAID to be tested and tested again, and I want it to use as little code as humanly possible. (E.g. Linux SW RAID [1])

5. ZFS is relatively new and it combines 3 layers that I personally prefer them to be separate. A simple bug in one of the bottom layers (say, the pool management layer) can spell an end to your data in an recoverable way. And with a file-system as complex and relatively immature as ZFS (compared to say, ext2/3 or NTFS), this a -major- flaw.

D. Last and not least, while ZFS is -a- solution to improving the resiliency of RAID arrays, in my view, the OS lock-in, patent issues (that prevent other OS from implementing ZFS), and less than ideal implementation makes ZFS a far from ideal solution.

- Gilboa
[1] $ cat /usr/src/kernels/linux/drivers/md/*raid*.[ch] | wc -l
13660

Edited 2010-01-19 17:47 UTC

Reply Parent Score: 2

RE[4]: RAID Z
by Laurence on Tue 19th Jan 2010 15:41 in reply to "RE[3]: RAID Z"
Laurence Member since:
2007-03-26

I'm not quick to dismiss ZFS.
I actually have a OpenSolaris VM w/ZFS on this machine (under Linux/KVM).

I am saying that ZFS is not the solution to everything.
It cannot replace hardware RAID controllers.


While I do see where you're coming from, I think you've over-racted to the opening post as nobody was suggesting that ZFS was the solution to everything.
We were just saying that currently there is a solution to the lack of triple parity RAID and that solution is ZFS. It was a very specific point he was making rather than the generalised "ZFS will solve world debt" type evangelical speak that you're (understandably) sick of reading.

Sure there's needs for other solutions and standards - nobody disagrees with that. But the fact remains that ZFS DOES address the triple parity problem.
So personal opinions of ZFS aside - the original poster was spot on with his comments


And last and not least, *Solaris is also an OS. And you don't select an OS just because it has a shiny file system.


Actually you do if the purpose of an OS is to serve files.

Choosing an OS is about selecting that system has the right tools to do it's specific job the best.
So if you need a server with a file system such as ZFS, then selecting *Solaris because of it's FS is the correct decision to make. Just as if you want a media centre, you'd be more interested in graphics and sound card support than it's file system.

Besides, you talk as if you can't get samba, apache, et al for *Solaris, which clearly isn't the case.

Reply Parent Score: 2

RE[5]: RAID Z
by gilboa on Tue 19th Jan 2010 17:40 in reply to "RE[4]: RAID Z"
gilboa Member since:
2005-07-06

While I do see where you're coming from, I think you've over-racted to the opening post as nobody was suggesting that ZFS was the solution to everything.
We were just saying that currently there is a solution to the lack of triple parity RAID and that solution is ZFS. It was a very specific point he was making rather than the generalised "ZFS will solve world debt" type evangelical speak that you're (understandably) sick of reading.


Guess I misread the initial post.
As you suggest, even though I'm using (mostly for tests and multi-platform support) Solaris and FreeBSD machines, and do appreciate ZFS, I'm somewhat tired of the general "ZFS is the new green" auto-posts.

As for what I have "against" ZFS, pleas read this:
http://www.osnews.com/thread?404962

Sure there's needs for other solutions and standards - nobody disagrees with that. But the fact remains that ZFS DOES address the triple parity problem.
So personal opinions of ZFS aside - the original poster was spot on with his comments


ZFS does solve this issue, but so does software RAID1 over two sets of RAID5/6. (Read: it greatly depends on your definition of what counts as a solution...)

One cannot ignore the fact that unlike a theoretical hardware RAID7 controller, ZFS/OpenSolaris combo is not suited for everybody - far from it.

- Gilboa

Reply Parent Score: 2

RE[4]: RAID Z
by Kebabbert on Tue 19th Jan 2010 17:33 in reply to "RE[3]: RAID Z"
Kebabbert Member since:
2007-07-27

Why can you not replace hardware raid controllers? Dont you know that ZFS protects against much errors than hardware raid? I would not trust hardware raid, actually.

Here is another presentation on Silent Corruption from the CERN guy (their large physics multi billion machines produces huge amounts of data, imagine corrupted data worth of billion of dollars). He concludes that checksums (hardware raid) is not enough. You need end-to-end checksum (ZFS). He talks about they get corrupted data on their Linux rack servers, silently:

https://indico.desy.de/getFile.py/access?contribId=65&sessionId=42&r...


Even better; here is a website explaining how bad raid-5 is, and lots of shortcomings hardware raid has:
www.baarf.com
Lots of sysadmins explains technical details there.

Edited 2010-01-19 17:36 UTC

Reply Parent Score: 2

RE[5]: RAID Z
by gilboa on Tue 19th Jan 2010 17:50 in reply to "RE[4]: RAID Z"
gilboa Member since:
2005-07-06

Forgive me for being blunt.
But you are the 2'nd man to post this link.
I'm well aware of silent corruption issues.

Never the less, if you have taken the time to read the rest of the thread before posting, you'd notice that I have fairly reasonable reasons for avoiding ZFS in production use, even though I do use Solaris.

- Gilboa

Edited 2010-01-19 17:56 UTC

Reply Parent Score: 2