How to Stop XenServer from Mounting /var/log
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@BRRABill said in How to Stop XenServer from Mounting /var/log:
@travisdh1 said
dd would take a long, long time if you have it copying something like /proc, /sys, or /dev.
Is it "safe" to run dd on a running boot disk? Why does it take so long?
Assuming so, but you know what happens when one assumes!
Yes, it is only reading, not writing. Reading things is always safe.
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@scottalanmiller said
Yes, it is only reading, not writing. Reading things is always safe.
Why does it take so long for those directories?
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@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
Yes, it is only reading, not writing. Reading things is always safe.
Why does it take so long for those directories?
dd reads block devices, not directories. It has no concept of directories.
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@scottalanmiller said
dd reads block devices, not directories. It has no concept of directories.
Then what is the significance/reason for the previous poster saying
"dd would take a long, long time if you have it copying something like /proc, /sys, or /dev." -
@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
dd reads block devices, not directories. It has no concept of directories.
Then what is the significance/reason for the previous poster saying
"dd would take a long, long time if you have it copying something like /proc, /sys, or /dev."
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
dd reads block devices, not directories. It has no concept of directories.
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@scottalanmiller said
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.
So using dd to clone a USB while running (which we were discussing) would clone differently that if you shut down the XS, and used a separate machine, such as @DustinB3403 originally posted?
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@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.
So using dd to clone a USB while running (which we were discussing) would clone differently that if you shut down the XS, and used a separate machine, such as @DustinB3403 originally posted?
Yes. A running system has things like /proc and /dev. I haven't experimented with cloning the actual block device (/dev/sdaX) instead of the mounted file system, but I don't know how well it would work if you're not doing it from an LVM snapshot.....
Speaking of which, please tell me that XenServer 7 uses LVM for it's important bits?
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@travisdh1 said
Yes. A running system has things like /proc and /dev. I haven't experimented with cloning the actual block device (/dev/sdaX) instead of the mounted file system, but I don't know how well it would work if you're not doing it from an LVM snapshot.....
So a lot of what was said in this thread about using dd for cloning the XS USB boot device is not necessarily true...
https://www.mangolassi.it/topic/9425/cloning-xenserver-on-usb-or-sd -
@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.
So using dd to clone a USB while running (which we were discussing) would clone differently that if you shut down the XS, and used a separate machine, such as @DustinB3403 originally posted?
No. Why do you feel that way?
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@travisdh1 said in How to Stop XenServer from Mounting /var/log:
@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.
So using dd to clone a USB while running (which we were discussing) would clone differently that if you shut down the XS, and used a separate machine, such as @DustinB3403 originally posted?
Yes. A running system has things like /proc and /dev. I haven't experimented with cloning the actual block device (/dev/sdaX) instead of the mounted file system, but I don't know how well it would work if you're not doing it from an LVM snapshot.....
Speaking of which, please tell me that XenServer 7 uses LVM for it's important bits?
dd clones the block device, not the file system hierarchy.
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@scottalanmiller said in How to Stop XenServer from Mounting /var/log:
@travisdh1 said in How to Stop XenServer from Mounting /var/log:
@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.
So using dd to clone a USB while running (which we were discussing) would clone differently that if you shut down the XS, and used a separate machine, such as @DustinB3403 originally posted?
Yes. A running system has things like /proc and /dev. I haven't experimented with cloning the actual block device (/dev/sdaX) instead of the mounted file system, but I don't know how well it would work if you're not doing it from an LVM snapshot.....
Speaking of which, please tell me that XenServer 7 uses LVM for it's important bits?
dd clones the block device, not the file system hierarchy.
Yeah, yet I've had problems using it to make a copy of a block device that is in use.
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@travisdh1 said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said in How to Stop XenServer from Mounting /var/log:
@travisdh1 said in How to Stop XenServer from Mounting /var/log:
@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.
So using dd to clone a USB while running (which we were discussing) would clone differently that if you shut down the XS, and used a separate machine, such as @DustinB3403 originally posted?
Yes. A running system has things like /proc and /dev. I haven't experimented with cloning the actual block device (/dev/sdaX) instead of the mounted file system, but I don't know how well it would work if you're not doing it from an LVM snapshot.....
Speaking of which, please tell me that XenServer 7 uses LVM for it's important bits?
dd clones the block device, not the file system hierarchy.
Yeah, yet I've had problems using it to make a copy of a block device that is in use.
Same, I tested this at home on my running XS server, to clone the boot-usb to another USB and upon trying to boot from the clone it fails.
Recommended solution: turn server off, and clone from a different system.
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I'm not trying to be argumentative. It's just that we're recommended X and Y, but it seems that they don't seem to work.
I'd like to come up with a set guideline of ... hey XS is great off USB, but THIS is what you have to do, and anything will crash your system.
It just seems like we are having a lot of system crashes or "yeah I tried this in my home/test lab and it didn't work" situations.
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@travisdh1 said in How to Stop XenServer from Mounting /var/log:
Yeah, yet I've had problems using it to make a copy of a block device that is in use.
That's a locking and access issue, in no way does it related to things like /proc though since those are not related to the block device.
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@DustinB3403 said in How to Stop XenServer from Mounting /var/log:
@travisdh1 said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said in How to Stop XenServer from Mounting /var/log:
@travisdh1 said in How to Stop XenServer from Mounting /var/log:
@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
Those are fake block devices. If you try to copy them they will take a very long time since /proc includes maps to the entire memory space and /dev includes all devices of any type including many mappings to every disk.
So using dd to clone a USB while running (which we were discussing) would clone differently that if you shut down the XS, and used a separate machine, such as @DustinB3403 originally posted?
Yes. A running system has things like /proc and /dev. I haven't experimented with cloning the actual block device (/dev/sdaX) instead of the mounted file system, but I don't know how well it would work if you're not doing it from an LVM snapshot.....
Speaking of which, please tell me that XenServer 7 uses LVM for it's important bits?
dd clones the block device, not the file system hierarchy.
Yeah, yet I've had problems using it to make a copy of a block device that is in use.
Same, I tested this at home on my running XS server, to clone the boot-usb to another USB and upon trying to boot from the clone it fails.
That may be because some blocks are in process of being changed and are not consistent.
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@BRRABill said in How to Stop XenServer from Mounting /var/log:
I'm not trying to be argumentative. It's just that we're recommended X and Y, but it seems that they don't seem to work.
I thought that the recommendation was to clone prior to boot time.
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@scottalanmiller said
I thought that the recommendation was to clone prior to boot time.
Is it? We've winded around it so much, I wasn't sure.
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@BRRABill said in How to Stop XenServer from Mounting /var/log:
@scottalanmiller said
I thought that the recommendation was to clone prior to boot time.
Is it? We've winded around it so much, I wasn't sure.
That's the only way that we've ever approached it. Meaning how we (NTG) deal with any cloning operations for production systems. If you want to clone while it is running you need it locked as read only, I'm pretty sure. Which you don't normally want to do while running.
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Coming back around to this, I had some time today, and threw the hard drive from the crashed system (the one that crashed when I added a folder to the SR) into my test XS setup.
Booted up fine, and everything seems to be OK. The drive from the crash is /dev/sdb
--- Physical volume --- PV Name /dev/sdb VG Name XSLocalEXT-40f7cced-9587-c38f-e152-057e4ec2b2d0 PV Size 447.13 GiB / not usable 14.84 MiB Allocatable yes (but full) PE Size 4.00 MiB Total PE 114462 Free PE 0 Allocated PE 114462 PV UUID pC2Rq6-pQ7S-rQr3-0eTq-d1OS-2Bnh-ot2ajP--- Volume group --- VG Name XSLocalEXT-40f7cced-9587-c38f-e152-057e4ec2b2d0 System ID Format lvm2 Metadata Areas 1 Metadata Sequence No 2 VG Access read/write VG Status resizable MAX LV 0 Cur LV 1 Open LV 0 Max PV 0 Cur PV 1 Act PV 1 VG Size 447.12 GiB PE Size 4.00 MiB Total PE 114462 Alloc PE / Size 114462 / 447.12 GiB Free PE / Size 0 / 0 VG UUID 3F38x8-Jz47-oaL9-oGSf-lGJb-tudH-mg0iB5lvs shows the LV. But when I go to /dev/mapper, it is not listed. This is the same thing that happened on the crashed server.
lvdisplay gives us a little more info
Googling around, I found the lvscan command, which gave me this.
inactive '/dev/XSLocalEXT-40f7cced-9587-c38f-e152-057e4ec2b2d0/40f7cced-9587-c38f-e152-057e4ec2b2d0' [447.12 GiB] inherit ACTIVE '/dev/XSLocalEXT-dba1e375-4e51-7e22-a64b-e7bcc39db67a/dba1e375-4e51-7e22-a64b-e7bcc39db67a' [465.75 GiB] inheritUh-oh ... inactive.
Doing some more Googling, it appears that
lvchange -a <LVname>
will reactivate it. Is that correct?Also, what typically would take a LV offline? That must have been what happened.
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Actually it was:
lvchange -ay <VGname/LVname>
