Alexey Fisher wrote:
Am Freitag, den 30.10.2009, 11:14 -0500 schrieb Eric Sandeen:
Alexey Fisher wrote:
Am Freitag, den 30.10.2009, 10:14 -0500 schrieb Eric Sandeen:
...
After a little brief digging I'm not sure when the xfs mount option went
in or why...
But for both
xfs: mount -o ro,norecovery
and
ext[34]: mount -o ro,noload
I don't think either one should touch the disk.
Also, both should skip journal replay if you set the block device
readonly prior to mount (hdparm -r can do this).
Interesting tip, thank you.
But there is some problems:
1. "hdparm -r" will set complete drive to ro mode. This is bad if i
use /dev/sda1 for root and /dev/sda5 need to be forced readonly.
So point it at the partition not the drive:
[root@neon ~]# hdparm -r 1 /dev/sda1
/dev/sda1:
setting readonly to 1 (on)
readonly = 1 (on)
[root@neon ~]# hdparm -r /dev/sda2
/dev/sda2:
readonly = 0 (off)
It doesn't change the hardware, it sets a flag on the kernel's block
device structure.
ok, got it. Every day learning something new.
It was not clear for me, after i read man hdparm: "Get/set read-only
flag for the device. When set, Linux disallows write operations on
the device."
2. the fact xfs and ext[3,4] use different options for true_ro make
things complicated.
the hazards of being an open source sysadmin I guess.
:( are there any plans to unify mount options?
Some of this gets done; barrier options now match across xfs & ext4, I'm
actually just writing a patch for ext3.
Doing the same for noload/norecovery would be pretty trivial.
3. the definition of ro is broken.
depends on what you mean by ro. A user can only read from the
filesystem so it is accurate in that respect. Is "ro" for the fs or the
bdev? Semantic differences but not necessarily broken.
Hmm... bdev. any chance to do temporary recovery and load it as external
journal if ro used? Anyway, you already pointed me to hdparm, so i can
use it too.
There were patches floated to in-ram recovery for those blocks so that
you could have a consistent fs w/o touching the disk but it didn't seem
to get far.
4. many frustrated admins who mounted part of raid1 only with "-o ro"
Dunno what you mean by that ...
raid1 is down, so you need for some reasons to mount ro only one disk of
the array. Needed to do it for short time (i used -o ro), now i know
this probably was a bad idea (bad me, should read documentation). Need
to check my raid now. Suddenly i'm not alone who doing this :(
oh I see. Yup....
-Eric
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