Re: Exactly what is wrong with RAID5/6

On 2017-06-23 13:25, Michał Sokołowski wrote: Hello group. I am confused: Can somebody please confirm/deny, which RAID subsystem is affected? BTRFS' RAID5/6 or mdadm (Linux kernel raid) RAID 5/6 ? All of the issues mentioned here are specific to BTRFS raid5/raid6 profiles, with the exception

Re: Exactly what is wrong with RAID5/6

Hello group. I am confused: Can somebody please confirm/deny, which RAID subsystem is affected? BTRFS' RAID5/6 or mdadm (Linux kernel raid) RAID 5/6 ? Are there some gotchas (in terms of broken reliability) when using kernel one? The web is full of legends, it seems that this confusion is quite

Re: Exactly what is wrong with RAID5/6

On 2017-06-22 04:12, Qu Wenruo wrote: > > And in that case even device of data stripe 2 is missing, btrfs don't really > need to use parity to rebuild it, as btrfs knows there is no extent in that > stripe, and data csum matches for data stripe 1. You are assuming that there is no data in

Re: Exactly what is wrong with RAID5/6

At 06/22/2017 10:43 AM, Chris Murphy wrote: On Wed, Jun 21, 2017 at 8:12 PM, Qu Wenruo wrote: Well, in fact, thanks to data csum and btrfs metadata CoW, there is quite a high chance that we won't cause any data damage. But we have examples where data does not

Re: Exactly what is wrong with RAID5/6

On Wed, Jun 21, 2017 at 8:12 PM, Qu Wenruo wrote: > > Well, in fact, thanks to data csum and btrfs metadata CoW, there is quite a > high chance that we won't cause any data damage. But we have examples where data does not COW, we see a partial stripe overwrite. And if

Re: Exactly what is wrong with RAID5/6

At 06/22/2017 02:24 AM, Chris Murphy wrote: On Wed, Jun 21, 2017 at 2:45 AM, Qu Wenruo wrote: Unlike pure stripe method, one fully functional RAID5/6 should be written in full stripe behavior, which is made up by N data stripes and correct P/Q. Given one example to

Re: Exactly what is wrong with RAID5/6

At 06/22/2017 01:03 AM, Goffredo Baroncelli wrote: Hi Qu, On 2017-06-21 10:45, Qu Wenruo wrote: At 06/21/2017 06:57 AM, waxhead wrote: I am trying to piece together the actual status of the RAID5/6 bit of BTRFS. The wiki refer to kernel 3.19 which was released in February 2015 so I assume

Re: Exactly what is wrong with RAID5/6

On Wed, Jun 21, 2017 at 2:12 PM, Goffredo Baroncelli wrote: > > Generally speaking, when you write "two failure" this means two failure at > the same time. But the write hole happens even if these two failures are not > at the same time: > > Event #1: power failure between

Re: Exactly what is wrong with RAID5/6

On 2017-06-21 20:24, Chris Murphy wrote: > On Wed, Jun 21, 2017 at 2:45 AM, Qu Wenruo wrote: > >> Unlike pure stripe method, one fully functional RAID5/6 should be written in >> full stripe behavior, which is made up by N data stripes and correct P/Q. >> >> Given one

Re: Exactly what is wrong with RAID5/6

On Wed, Jun 21, 2017 at 12:51 AM, Marat Khalili wrote: > On 21/06/17 06:48, Chris Murphy wrote: >> >> Another possibility is to ensure a new write is written to a new*not* >> full stripe, i.e. dynamic stripe size. So if the modification is a 50K >> file on a 4 disk raid5; instead of

Re: Exactly what is wrong with RAID5/6

On Wed, Jun 21, 2017 at 2:45 AM, Qu Wenruo wrote: > Unlike pure stripe method, one fully functional RAID5/6 should be written in > full stripe behavior, which is made up by N data stripes and correct P/Q. > > Given one example to show how write sequence affects the

Re: Exactly what is wrong with RAID5/6

On 2017-06-21 13:20, Andrei Borzenkov wrote: 21.06.2017 16:41, Austin S. Hemmelgarn пишет: On 2017-06-21 08:43, Christoph Anton Mitterer wrote: On Wed, 2017-06-21 at 16:45 +0800, Qu Wenruo wrote: Btrfs is always using device ID to build up its device mapping. And for any multi-device

Re: Exactly what is wrong with RAID5/6

21.06.2017 16:41, Austin S. Hemmelgarn пишет: > On 2017-06-21 08:43, Christoph Anton Mitterer wrote: >> On Wed, 2017-06-21 at 16:45 +0800, Qu Wenruo wrote: >>> Btrfs is always using device ID to build up its device mapping. >>> And for any multi-device implementation (LVM,mdadam) it's never a >>>

Re: Exactly what is wrong with RAID5/6

21.06.2017 09:51, Marat Khalili пишет: > On 21/06/17 06:48, Chris Murphy wrote: >> Another possibility is to ensure a new write is written to a new*not* >> full stripe, i.e. dynamic stripe size. So if the modification is a 50K >> file on a 4 disk raid5; instead of writing 3 64K data strips + 1 64K

Re: Exactly what is wrong with RAID5/6

Hi Qu, On 2017-06-21 10:45, Qu Wenruo wrote: > At 06/21/2017 06:57 AM, waxhead wrote: >> I am trying to piece together the actual status of the RAID5/6 bit of BTRFS. >> The wiki refer to kernel 3.19 which was released in February 2015 so I assume >> that the information there is a tad outdated

Re: Exactly what is wrong with RAID5/6

On 2017-06-21 08:43, Christoph Anton Mitterer wrote: On Wed, 2017-06-21 at 16:45 +0800, Qu Wenruo wrote: Btrfs is always using device ID to build up its device mapping. And for any multi-device implementation (LVM,mdadam) it's never a good idea to use device path. Isn't it rather the other

Re: Exactly what is wrong with RAID5/6

On Wed, 2017-06-21 at 16:45 +0800, Qu Wenruo wrote: > Btrfs is always using device ID to build up its device mapping. > And for any multi-device implementation (LVM,mdadam) it's never a > good  > idea to use device path. Isn't it rather the other way round? Using the ID is bad? Don't you remember

Re: Exactly what is wrong with RAID5/6

At 06/21/2017 06:57 AM, waxhead wrote: I am trying to piece together the actual status of the RAID5/6 bit of BTRFS. The wiki refer to kernel 3.19 which was released in February 2015 so I assume that the information there is a tad outdated (the last update on the wiki page was July 2016)

Re: Exactly what is wrong with RAID5/6

> [ ... ] This will make some filesystems mostly RAID1, negating > all space savings of RAID5, won't it? [ ... ] RAID5/RAID6/... don't merely save space, more precisely they trade lower resilience and a more anisotropic and smaller performance envelope to gain lower redundancy (= save space). --

Re: Exactly what is wrong with RAID5/6

On 21/06/17 06:48, Chris Murphy wrote: Another possibility is to ensure a new write is written to a new*not* full stripe, i.e. dynamic stripe size. So if the modification is a 50K file on a 4 disk raid5; instead of writing 3 64K data strips + 1 64K parity strip (a full stripe write); write out 1

Re: Exactly what is wrong with RAID5/6

On Tue, Jun 20, 2017 at 5:25 PM, Hugo Mills wrote: > On Wed, Jun 21, 2017 at 12:57:19AM +0200, waxhead wrote: >> I am trying to piece together the actual status of the RAID5/6 bit of BTRFS. >> The wiki refer to kernel 3.19 which was released in February 2015 so >> I assume

Re: Exactly what is wrong with RAID5/6

On Wed, Jun 21, 2017 at 12:57:19AM +0200, waxhead wrote: > I am trying to piece together the actual status of the RAID5/6 bit of BTRFS. > The wiki refer to kernel 3.19 which was released in February 2015 so > I assume that the information there is a tad outdated (the last > update on the wiki page

Exactly what is wrong with RAID5/6

I am trying to piece together the actual status of the RAID5/6 bit of BTRFS. The wiki refer to kernel 3.19 which was released in February 2015 so I assume that the information there is a tad outdated (the last update on the wiki page was July 2016)