Hi guys,
I saw a bunch of discussion of devices changing names when hot-plugged.
If you get the device name right when you add it to the array first, all
is good since the superblock is used to "discover" the device later.
However, to make things easier/clearer, and to avoid errors, one can
take a look at the set of directories:
/dev/disk/by-id
/dev/disk/by-path
/dev/disk/by-uuid
/dev/disk/by-label
for a predictable, more static view of the drives. The symlinks in these
directories are created by udev, and are simply links to the "real"
device nodes /dev/sd{a-z}*. You can either just use these symlinks as a
way of verifying that you are adding the right device, or add the device
using the symlink.
At our location, we even augmented udev to add links to labeled GPT
partitions in /dev/disk/by-label, and now our drives/partitions look
like this:
iscsi00-drive00-part00 -> ../../sda1
iscsi00-drive01-part00 -> ../../sdb1
iscsi00-drive02-part00 -> ../../sdc1
iscsi00-drive03-part00 -> ../../sdd1
iscsi00-drive04-part00 -> ../../sde1
This way, we know exactly which bay contains exactly which drive, and it
stays this way. If you guys want, I can share with you the changes to
udev necessary and the script which extracts the GPT label and reports
it to udev for this magic to happen :). Please reply to this thread with
a request if you think it may be useful to you.
Cheers,
Iordan
On 02/23/11 17:13, Roberto Nunnari wrote:
Roberto Spadim wrote:
hum, maybe you are using mdadm.conf or autodetect, non autodetect
should be something like this:
i donÂt know the best solution, but it works ehhehe
kernel /vmlinuz-2.6.9-89.31.1.ELsmp ro root=/dev/md0 rhgb
quiet md=0,/dev/sda,/dev/sdb md=1,xxxx,yyyy.....
or another md array...
humm i readed the sata specification and removing isnÂt a problem, at
eletronic level the sata channel is only data, no power source, all
channels are diferencial (like rs422 or rs485), i donÂt see anyproblem
removing it. i tryed hot plug a revodrive (pciexpress ssd) and it
donÂt work (reboot) hehehe, pci-express isnÂt hot plug =P, sata2 donÂt
have problems, the main problem is a short circuit at power source, if
you remove with caution no problems =)
i tried in some others distros and udev created a new device when add
a diferent disk for example, remove sdb, and add another disk create
sdc (not sdb), maybe with another udev configuration should work
Ok. I'll keep all that in mind tomorrow.
Best regards.
Robi
2011/2/23 Roberto Nunnari <roberto.nunnari@xxxxxxxx>:
Roberto Spadim wrote:
i donÂt know how you setup your kernel (with or without raid
I use the official CentOS kernel with no modification and don't
know about raid autodetect, but:
# cat /boot/config-2.6.24-28-server |grep -i raid
CONFIG_BLK_DEV_3W_XXXX_RAID=m
CONFIG_MD_RAID0=m
CONFIG_MD_RAID1=m
CONFIG_MD_RAID10=m
CONFIG_MD_RAID456=m
CONFIG_MD_RAID5_RESHAPE=y
CONFIG_MEGARAID_LEGACY=m
CONFIG_MEGARAID_MAILBOX=m
CONFIG_MEGARAID_MM=m
CONFIG_MEGARAID_NEWGEN=y
CONFIG_MEGARAID_SAS=m
CONFIG_RAID_ATTRS=m
CONFIG_SCSI_AACRAID=m
autodetect?) do you use kernel command line to setup raid? autodetect?
/dev/md0 in grub
I don't know if that means autodetect, but I guess so..
here in my test machine iÂm using kernel command line (grub), i donÂt
have a server with hotplug bay, i open the case and remove the wire
with my hands =) after reconecting it with another device kerenel
Is it safe? Isn't it a blind bet to fry up the controller and/or disk?
recognize the new device reread the parititions etc etc and i can add
it to array again
my grub is something like:
md=0,/dev/sda,/dev/sdb .....
internal meta data, raid1, i didnÂt like the autodetect (itÂs good)
but i prefer hardcoded kernel command line (itÂs not good with usb
devices)
the relevant part of my grub is:
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.9-89.31.1.ELsmp)
root (hd0,0)
kernel /vmlinuz-2.6.9-89.31.1.ELsmp ro root=/dev/md0 rhgb quiet
initrd /initrd-2.6.9-89.31.1.ELsmp.img
Best regards.
Robi
2011/2/23 Roberto Nunnari <roberto.nunnari@xxxxxxxx>:
Roberto Spadim wrote:
sata2 without hot plug?
Hi Roberto.
I mean that there is no hot-plug bay, with sliding rails etc..
The drives are connected to the mb using standard sata cables.
check if your sda sdb sdc will change after removing it, itæ depends
on your udev or another /dev filesystem
Ok, thank you.
That means that if I take care to check the above, and
the new drive will be sdb, then taking the steps indicated
in my original post will do the job?
Best regards.
Robi
2011/2/23 Roberto Nunnari <roberto.nunnari@xxxxxxxx>:
Hello.
I have a linux box, with two 2TB sata HD in raid 1.
Now, one disk is in failed state and it has no spares:
# cat /proc/mdstat
Personalities : [raid1]
md1 : active raid1 sdb4[2](F) sda4[0]
1910200704 blocks [2/1] [U_]
md0 : active raid1 sdb1[1] sda2[0]
40957568 blocks [2/2] [UU]
unused devices: <none>
The drives are not hot-plug, so I need to shutdown the box.
My plan is to:
# sfdisk -d /dev/sdb > sdb.sfdisk
# mdadm /dev/md1 -r /dev/sdb4
# mdadm /dev/md0 -r /dev/sdb1
# shutdown -h now
replace the disk and boot (it should come back up, even without one
drive,
right?)
# sfdisk /dev/sdb < sdb.sfdisk
# mdadm /dev/md1 -a /dev/sdb4
# mdadm /dev/md0 -a /dev/sdb1
and the drives should start to resync, right?
This is my first time I do such a thing, so please, correct me
if the above is not correct, or is not a best practice for
my configuration.
My last backup of md1 is of mid november, so I need to be
pretty sure I will not lose my data (over 1TB).
A bit abount my environment:
# mdadm --version
mdadm - v1.12.0 - 14 June 2005
# cat /etc/redhat-release
CentOS release 4.8 (Final)
# uname -rms
Linux 2.6.9-89.31.1.ELsmp i686
Thank you very much and best regards.
Robi
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