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Comment Re:BTRFS is getting there (Score 1) 267

Raid 5 spreads the parity across the array. (Raid 5 is striping with parity). You're thinking of raid 4.

Thank you. Error accepted. I got bitten by some bad material on the web. What ZFS does do differently is this: every (variable size) logical block written is its own stripe. It does not have a fixed stripe size like RAID5, which more than one block may share. This eliminates some read-modifiy-writes which RAID5 has to do (with the attendant reduction in throughput), as well as being instrumental in closing the write hole. It can do this because the redundancy is implemented at the same level as the filesystem. I.e., it is aware of the data structure, which traditional RAID5 is not.

Comment Re:BTRFS is getting there (Score 1) 267

rahvin112 - You are unquestionably mistaken about the write hole. The design and implementation of ZFS specifically banishes it. Other respondents have made this clear with some authority, and I will only add this reference:

"RAID-Z is a data/parity scheme like RAID-5, but it uses dynamic stripe width. Every block is its own RAID-Z stripe, regardless of blocksize. This means that every RAID-Z write is a full-stripe write. This, when combined with the copy-on-write transactional semantics of ZFS, completely eliminates the RAID write hole. RAID-Z is also faster than traditional RAID because it never has to do read-modify-write."

Now, it is quite conceivable to me that BTRFS could possibly achieve a similar result, if it melds redundancy at the file system level as ZFS does, and uses similar careful design. But NOT just by the fact of implementing RAID5, which I read as your claim.

brambus has an excellent response which I am sure you have seen. He corrects some mis-speaks of my own, which are a bit at the detail level, including precisely how ZFS closes the write hole. So it doesn't finish the metadata update and then the data update. It instead atomically sets a pointer to the updated COW writes at the end. Either you get the uncorrupted "before", or the uncorrupted "after", depending on exactly when your power fails.

Comment Re:Not the total cost! (Score 2) 415

Are you going to overbuild the whole system 4x so that the 25% receiving good wind can drive all the rest of it? Are you going to make the grid so robust, so grossly overbuilt, that you can ship huge amounts of power over transcontinental distances, rather than just small balancing compensations? There will be enormous costs associated with that collossal effort.

Comment Re:BTRFS is getting there (Score 2, Informative) 267

I don't know what your definition of "significant" is, but the BTRFS wiki says "The one missing piece, from a reliability point of view, is that it is still vulnerable to the parity RAID 'write hole', where a partial write as a result of a power failure may result in inconsistent parity data." ZFS RAIDZ is expressly free from the write hole. That is very significant to me.

RAIDZ's write hole advantage is a product of three specifics: (1) RAID5 has n data disks plus one dedicated parity-only disk; ZFS distributes all data and all parity across all disks - (2) ZFS updates metadata before data; RAID5 has no concept of metadata - and (3) COW (both have this).

And before you object "but UPS" - UPSs and power supplies can fail, too - and a kernel panic is essentially a "power failure" too; one which a UPS is powerless to prevent.

If that Wiki should be out of date, you can show me something that isn't, but all I find out there is a lot of outdated stuff.

Comment Re:BTRFS is getting there (Score 1) 267

What do you mean it scales as you add more disks? You can't add disks to a ZFS array. You can replace them with bigger disks, but not just add them.

Wrong. You can't scale a pool by adding VDEVs to the existing pool, but you can expand without practical limit by generating VDEVs out of VDEVs and adding them. E.g., if you have 6 drives in a RAIDZ2, you can build a RAIDZ2 out of 6 (or some other number of) RAIDZ2s, including your original and 5 new ones. The downtime when you switch over to your expanded config is minimal. Think in terms of a minute or two if you plan right. The pool array setup is a background and incremental process, and the pool is available to start using essentially immediately. And your existing data is seamlessly preserved in place. You don't have to back up and restore. That's just an example.

In fact using a gigantic number of drives in a scalar array goes against good practice in ZFS and in other file systems. There is no real limit to how hierarchical your structure can be in ZFS, and still reduce to a single root (if you so wish).

The basic building block in ZFS is the VDEV. You make your striped, or mirrored, or striped-and-mirrored, or RAIDZ1 (single parity), RAIDZ2 (double parity), or RAIDZ3 (triple parity) array out of VDEVs, which can be whole drives, partitions, files, or VDEVs themselves. You can use any combination of any of these kinds of arrays as your VDEVs in your higher-level array.

If you play a game of trying to knock ZFS's design and capabilities, you will lose.

Comment Re:Laughable (Score 1) 203

Do you have a point, or are you just butthurt that not everyone has the same starry-eyed worship for capitalism?

You sure as HELL don't seem to be conversant with what it takes to pay the unconscionably through-the-roof costs of feeding yourself and warming yourself in the winter. Food prices and heating oil prices are through the roof. I don't thank selfish bastards for making themselves rich at my unavoidable expense. It's called realism, son.

Comment Re:Laughable (Score 3, Insightful) 203

Google is just doing what any corporation does. The bottom line is their own aggrandizement. Anything they can get away with to that end they will do. Why do you have this fantasy that they are special?

Capitalism is all about strife and self-interest. It's inherent in the system. You can but-but that by bringing up the "invisible hand of the market", but it is a truism.

Comment Re:This ruling won't fix anything (Score 3, Informative) 203

being a US company

These gigantic corporations are not "U.S. companies" by any stretch of the imagination - if that term even has any meaning at all any more. They are me-first entities whose only allegiance is to themselves, and they operate globally with complete cynicism. If they can't defy regulations in secret (VW?) or win their case in court (Microsoft) or co-opt authorities and get regulations changed openly or behind the curtain, they will accommodate the players who are large enough that their citizens and corporations can't be forgone as customers. And that certainly includes both Europe and the U.S.

Comment Re:This ruling won't fix anything (Score 1) 203

Optimistic USian here, still behind prodding my government back to a place worthy of repect in the World

You don't think Trump or any of the other likely Republican contenders would fundamentally change this stuff, do you? I happen to believe Cruz and possibly Paul would have some effect, but neither one has a snowball's chance in hell of getting anywhere. Certainly Clinton or Biden would wholeheartedly continue the lowering of the dark curtain over the U.S. Sanders I think would try to make meaningful changes but get nowhere against Congress.

if we don't improve out international reputation, we won't long have as many European allies

The U.S. is already a sick joke throughout the world, including Europe. This declaration reinforces that.

Comment Re:Obvious ruling (Score 1, Insightful) 203

the companies in question are found to be colluding with criminal organizations like the NSA

I like the way you express yourself. The problem is that every citizen of the United States is in collusion with a rogue illegitimate government operating in blatant disregard for its own goddam Constitution and in open enmity to the people, for countenancing this abomination of an oligarchy without rising up and overthrowing it. Certainly the voters are, every time they vote for an establishment cog to be part of the vast conspiracy.

Just to make it clear that this is an observation, not a rallying cry, I am too, because I can't even imagine myself in open rebellion. Such is the way the ascendancy of evil undermines vitality.

Real Programs don't use shared text. Otherwise, how can they use functions for scratch space after they are finished calling them?