RE: Forcing raid1 resync

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 > -----Original Message-----
> From: Guy [mailto:bugzilla@xxxxxxxxxxxxxxxx] 
> Sent: Monday, August 16, 2004 12:49 PM
> To: 'Guy'; Rechenberg, Andrew; linux-raid@xxxxxxxxxxxxxxx
> Subject: RE: Forcing raid1 resync
> 
> Spelling/typo error....
> 
> >From what I understand...
> If the arrays don't share physical disks, they can re-sync at 
> the same time.
> Maybe some throttling system is limiting it to just 5 at a 
> time.  Maybe CPU load?  I don't know if md does things based 
> on how busy the CPU is.  Is your CPU maxed out?


The box in question is a quad Xeon 1.4GHz with HT enabled.  I don't
believe it was CPU bound.  When I initially created the arrays they all
started their re-sync at the same time.


> 
> These are related to throttling:
> /proc/sys/dev/raid/speed_limit_max
> /proc/sys/dev/raid/speed_limit_min
> 
> Do "man md" for more info.
> 
> The speed limits are per device, not per array.
> Make sure the max is large enough the permit your disks to go 
> as fast as they can.  I use 100000 (100,000K bytes/second).  
> My disks are not that fast, and having too large of a number 
> does not hurt.
> At least as a test, set the min to the same value as max.
> 
> I use these commands when I want to change by hand:
> cat /proc/sys/dev/raid/speed_limit_max
> cat /proc/sys/dev/raid/speed_limit_min
> 
> echo 100000 > /proc/sys/dev/raid/speed_limit_max
> echo 1000 > /proc/sys/dev/raid/speed_limit_min



Yep, I already have those commands in my rc.local so they get reloaded
upon reboot.


> 
> Guy
> 
> -----Original Message-----
> From: linux-raid-owner@xxxxxxxxxxxxxxx
> [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of 
> Rechenberg, Andrew
> Sent: Monday, August 16, 2004 11:24 AM
> To: linux-raid@xxxxxxxxxxxxxxx
> Subject: Forcing raid1 resync
> 
> Hello,
> 
> Is there anyway to force a resync of RAID1 arrays that need 
> to be resynced?  I have 26 RAID1 arrays and when the system 
> shuts down uncleanly, or the machine crashes hard, sometimes 
> I need to hotadd devices back into the array.  For example if 
> I have the following in
> /etc/raidtab:
> 
> raiddev /dev/md23
>         raid-level              1
>         nr-raid-disks           2
>         persistent-superblock   1
>         chunk-size              64
>  
>         device                  /dev/sdao1
>         raid-disk               0
>         device                  /dev/sdbc1
>         raid-disk               1
> 
> /proc/mdstat for md23 will show:
> 
> md23 : active raid1 sdbc1[1]
>       17783808 blocks [2/2] [U_]
> 
> And I will need to use mdadm or raidhotadd to add /dev/sdao1 
> back into the array.  When I add a device back into the array 
> the reconstruction doesn't start immediately and/or if 
> another reconstruction is underway, the new recontruction 
> will not occur until the first one has completed.
> 
> Is this behavior expected/by design?  Waiting for 26 arrays 
> to reconstruct one at a time is painfully slow.  When I 
> created the arrays they all started to sync at the same time 
> so I know the RAID code will sync more than one at a time, 
> and when my box came up yesterday after a hard power cycle, 
> about 5 arrays started syncing, but the rest waited until 
> those were finished and then synced one at a time.
> 
> I looked through md.c and raid1.c and I see that hot_add_disk() calls
> md_recover_arrays() which wakes up the md recovery thread, 
> but does the thread only allow one synchronization to occur at a time?
> 
> Here are some of my system details:
> 
> Red Hat 7.3 with updates
> kernel-bigmem-2.4.20-30 with megaraid2 patch
> 
> If someone could point me in the direction in the code to 
> understand the way this process works I would appreciate it.  
> Let me know if you need any more information.
> 
> Regards,
> Andrew Rechenberg
> Infrastructure Team, Sherman Financial Group
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