Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Richard Elling
On Jan 15, 2012, at 8:49 PM, Bob Friesenhahn wrote: > On Sun, 15 Jan 2012, Edward Ned Harvey wrote: >> >> Such failures can happen undetected with or without ECC memory. It's simply >> less likely with ECC. The whole thing about ECC memory... It's just doing >> parity. It's a very weak checks

Re: [zfs-discuss] Data loss by memory corruption?

2012-01-15 Thread Richard Elling
On Jan 14, 2012, at 6:36 AM, Stefan Ring wrote: > Inspired by the paper "End-to-end Data Integrity for File Systems: A > ZFS Case Study" [1], I've been thinking if it is possible to devise a way, > in which a minimal in-memory data corruption would cause massive data > loss. For enterprise-class

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Richard Elling
On Jan 15, 2012, at 7:04 AM, Jim Klimov wrote: > "Does raidzN actually protect against bitrot?" > That's a kind of radical, possibly offensive, question formula > that I have lately. Simple answer: no. raidz provides data protection. Checksums verify data is correct. Two different parts of the st

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Bob Friesenhahn
On Sun, 15 Jan 2012, Edward Ned Harvey wrote: Such failures can happen undetected with or without ECC memory. It's simply less likely with ECC. The whole thing about ECC memory... It's just doing parity. It's a very weak checksum. If corruption happens in memory, it's I am beginning to be

Re: [zfs-discuss] zfs defragmentation via resilvering?

2012-01-15 Thread Bob Friesenhahn
On Sun, 15 Jan 2012, Edward Ned Harvey wrote: While I'm waiting for this to run, I'll make some predictions: The file is 2GB (16 Gbit) and the disk reads around 1Gbit/sec, so reading the initial sequential file should take ~16 sec After fragmentation, it should be essentially random 4k fragments

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Edward Ned Harvey
> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Gary Mills > > There's actually no such thing as bitrot on a disk. Each sector on > the disk is accompanied by a CRC that's verified by the disk > controller on each read. It will either retu

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Edward Ned Harvey
> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Jim Klimov > > 2012-01-15 19:38, Edward Ned Harvey wrote: > >> 1) How does raidzN protect agaist bit-rot without known full > >>death of a component disk, if it at all does? > > zfs can

Re: [zfs-discuss] zfs defragmentation via resilvering?

2012-01-15 Thread Edward Ned Harvey
> From: Bob Friesenhahn [mailto:bfrie...@simple.dallas.tx.us] > > On Thu, 12 Jan 2012, Edward Ned Harvey wrote: > > Suppose you have a 1G file open, and a snapshot of this file is on disk from > > a previous point in time. > > for ( i=0 ; i<1trillion ; i++ ) { > > seek(random integer in range[

[zfs-discuss] Apple's ZFS-alike - Re: Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Toby Thain
On 15/01/12 10:38 AM, Edward Ned Harvey wrote: ... Linux is going with btrfs. MS has their own thing. Oracle continues with ZFS closed source. Apple needs a filesystem that doesn't suck, but they're not showing inclinations toward ZFS or anything else that I know of. Rumours have long circu

Re: [zfs-discuss] Data loss by memory corruption?

2012-01-15 Thread Bob Friesenhahn
On Sun, 15 Jan 2012, Jim Klimov wrote: It does seem possible that in-memory corruption of data payload and/or checksum of a block before writing it to disk would render it invalid on read (data doesn't match checksum, ZFS returns EIO) . Maybe even worse if the in-memory block is corrupted before

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Jim Klimov
2012-01-15 20:43, Gary Mills пишет: On Sun, Jan 15, 2012 at 04:06:33PM +, Peter Tribble wrote: On Sun, Jan 15, 2012 at 3:04 PM, Jim Klimov wrote: "Does raidzN actually protect against bitrot?" That's a kind of radical, possibly offensive, question formula that I have lately. Yup, it does

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Andrew Gabriel
Gary Mills wrote: On Sun, Jan 15, 2012 at 04:06:33PM +, Peter Tribble wrote: On Sun, Jan 15, 2012 at 3:04 PM, Jim Klimov wrote: "Does raidzN actually protect against bitrot?" That's a kind of radical, possibly offensive, question formula that I have lately. Yup, it does. Th

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Gary Mills
On Sun, Jan 15, 2012 at 04:06:33PM +, Peter Tribble wrote: > On Sun, Jan 15, 2012 at 3:04 PM, Jim Klimov wrote: > > "Does raidzN actually protect against bitrot?" > > That's a kind of radical, possibly offensive, question formula > > that I have lately. > > Yup, it does. That's why many of us

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Jim Klimov
2012-01-15 20:06, Peter Tribble wrote: (Try writing over one half of a zfs mirror with dd and watch it cheerfully repair your data without an actual error in sight.) Are you certain it always works? AFAIK, mirror reads are round-robined (which leads to parallel read performance boosts). Only if

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Bob Friesenhahn
On Sun, 15 Jan 2012, Jim Klimov wrote: 1) How does raidzN protect agaist bit-rot without known full death of a component disk, if it at all does? Or does it only help against "loud corruption" where the disk reports a sector-access error or dies completely? Here is a layman's answer sinc

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Jim Klimov
2012-01-15 19:38, Edward Ned Harvey wrote: >> 1) How does raidzN protect agaist bit-rot without known full >>death of a component disk, if it at all does? > zfs can read disks 1,2,3,4... Then read disks 1,2,3,5... > Then read disks 1,2,4,5... ZFS can figure out which disk > returned the faul

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Peter Tribble
On Sun, Jan 15, 2012 at 3:04 PM, Jim Klimov wrote: > "Does raidzN actually protect against bitrot?" > That's a kind of radical, possibly offensive, question formula > that I have lately. Yup, it does. That's why many of us use it. > The way I get it, RAID5/6 generally has no mechanism to detect

Re: [zfs-discuss] RaidzN + mirror

2012-01-15 Thread Jim Klimov
2012-01-15 19:16, Edward Ned Harvey пишет: From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- boun...@opensolaris.org] On Behalf Of Jim Klimov 2) In particular, if I wanted to make a mirror of raidzN's, can it be done in one ZFS pool, or would I have to play with iSCSI and ZVOLs? A

Re: [zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Edward Ned Harvey
> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Jim Klimov > > 1) How does raidzN protect agaist bit-rot without known full > death of a component disk, if it at all does? > Or does it only help against "loud corruption" where the >

[zfs-discuss] ZFS Metadata on-disk grouping

2012-01-15 Thread Jim Klimov
Does ZFS currently attempt to group metadata in large sector-ranges on the disk? Can this be expected to happen "automagically" - i.e. during each TXG close we have to COW-update whole branches of the blockpointer tree, so these new blocks might "just happen" to always coalesce into larger sector

Re: [zfs-discuss] RaidzN + mirror

2012-01-15 Thread Edward Ned Harvey
> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Jim Klimov > > 2) In particular, if I wanted to make a mirror of raidzN's, > can it be done in one ZFS pool, or would I have to play > with iSCSI and ZVOLs? Although you can probably do someth

[zfs-discuss] Does raidzN actually protect against bitrot? If yes - how?

2012-01-15 Thread Jim Klimov
"Does raidzN actually protect against bitrot?" That's a kind of radical, possibly offensive, question formula that I have lately. Reading up on theory of RAID5, I grasped the idea of the write hole (where one of the sectors of the stripe, such as the parity data, doesn't get written - leading to

[zfs-discuss] RaidzN + mirror

2012-01-15 Thread Jim Klimov
How nested can be the VDEV tree? All the examples I've seen suggested 3 layers - root vdev, striping over some top-level vdevs (if present), made (redundantly) of some physical/leaf vdevs. In trivial cases this goes down to two levels (a root striping over non-redundant leaf vdevs) or one lev

Re: [zfs-discuss] Data loss by memory corruption?

2012-01-15 Thread Jim Klimov
2012-01-14 18:36, Stefan Ring wrote: Inspired by the paper "End-to-end Data Integrity for File Systems: A ZFS Case Study" [1], I've been thinking if it is possible to devise a way, in which a minimal in-memory data corruption would cause massive data loss. I could imagine a scenario where an enti