Doesn't "writes" do what resync does ?

Hi List,

As per my previous email, I am busy shifting a bunch of data around. I have just created a new RAID1 set, following which MD started resyncing it.

Before that completed, I started shifting data onto it. I always thought that writing data to a new array, does "exactly" what resyncing does (it has to do all the same calcs etc)

This doesn't seem to be the case:

md2 : active raid1 sdd2[1] sda2[0]

      243567616 blocks super 1.2 [2/2] [UU]
      [===>.................]  resync = 17.2% (41949184/243567616)

finish=122.3min speed=27454K/sec

yet:

--- Physical volume ---

  PV Name               /dev/md2
  VG Name               RAID
  PV Size               232.28 GiB / not usable 35.00 MiB
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              59456
  Free PE               811
  Allocated PE          58645
  PV UUID               my6BsX-cSPD-MTKK-8U0t-ULVl-MKcA-LcAW2D

All the data on here was moved from another RAID device and currently contains about 200gig of data.

Should that resync not have had more completed ?

Quoted 2 lines · Pieter De Wit

<snip>
Should that resync not have had more completed ?

Your question is invalid. What you meant to ask is

"Why are pvdisplay and mdstat reporting what seems to be conflicting state data?"

Did you also ask on the lvm list why pvdisplay says most PEs are consumed, yet mdstat says resync is only 17% complete?

Quoted 11 lines · Stan Hoeppner

Quoted 2 lines · Pieter De Wit

<snip>
Should that resync not have had more completed ?

Your question is invalid. What you meant to ask is

"Why are pvdisplay and mdstat reporting what seems to be conflicting state data?"

Did you also ask on the lvm list why pvdisplay says most PEs are consumed, yet mdstat says resync is only 17% complete?

Hi again Stan,

pvdisplay says most PEs are consumed because I moved that data to the device. My question, rephased then:

Shouldn't writes to a RAID device count as resyncs ?

Quoted 12 lines · Pieter De Wit

Quoted 11 lines · Stan Hoeppner

Quoted 2 lines · Pieter De Wit

<snip>
Should that resync not have had more completed ?

Your question is invalid. What you meant to ask is

"Why are pvdisplay and mdstat reporting what seems to be conflicting state data?"

Did you also ask on the lvm list why pvdisplay says most PEs are consumed, yet mdstat says resync is only 17% complete?

Quoted 6 lines

Hi again Stan,

pvdisplay says most PEs are consumed because I moved that data to the device. My question, rephased then:

Shouldn't writes to a RAID device count as resyncs ?

The resync process is independent of normal IO. It starts at the beginning and soldiers on to the end doing a read of each sector pair then comparing them (for RAID1). So no, writes don't count as resync operations. md doesn't perform write/read/verify in normal operation, only write. Linux relies on hardware to report write errors, and assumes the data hit the disk intact if no error. There is no mechanism to pass a new write as verified to the resync process. If you think it should you may want to shoot the idea past Neil. Though I'm sure he's already considered that and rejected it for various reasons.

And unless you restart the resync, it won't verify any sectors you wrote up to its current position. Any sectors you wrote after that point it will be verifying. You don't need to restart the resync or do another one. I'm simply explaining how the resync is independent of normal write IO.