Skip to main content

linux - mdadm & raid6: does "re-create(with different chunk size) + resync" destroy orig. data?

I would like to rescue data on my software raid-6 array. I did some stupid actions (described bellow) with this original array.



Main Question:




I need to know if original data stored on raid-6 array are definitely lost (or not) after the following actions have been prepared upon this array (executed in the order listed bellow):




  1. zeroing super-blocks of all the
    active disks/partitions registered
    in the array


  2. executing the "mdadm --create ..."
    command using different options
    (see bellow for list) than have been

    used when array have been created
    originally:
    -> different chunk size
    -> different layout
    -> different disks order


  3. resync-ing the array




Note: Specific values of mdadm parameters should not be relevant here, since this is about the principle how mdadm works ...




I think points 1) & 2) should not even touch the original data since they are supposed to manipulate just superblocks



I see the 3) point as most critical from data lost point of view: I'm not sure what exactly is happening with array during resync, but based on heavy activity of all involved hard drives (for ~7 hours) I assume the data storage area is completely re-processed ...



Sub-questions:




  1. Does ordering of hard drives/partitions (as they are ordered on mdadm command line) play role for raid6 creation & initial resync?


  2. What everything is necessary to backup after array creation to be able to safely re-create the array in similar situation as my is (e.g. backup superblocks informations & partition table info for each disk involved in the array ...)?





Comment:



The mdadm wiki article (http://en.wikipedia.org/wiki/Mdadm) should be revised and author should be kicked in to ass a little bit, or more then just a little bit ...
The article mentions the zeroing superblocks & subsequent array re-creation as solution for getting rid of the "mdadm: Cannot open ...: Device or resource busy" issue.
Author somehow forgot to mention important step - to backup the parameters the original array (superblocks) as the first step ... and also my investigation seems to point out that the ordering of the involved disks/partitions plays role as well ...



Thanks for answers,
Peter

Comments

Post a Comment

Popular posts from this blog

linux - iDRAC6 Virtual Media native library cannot be loaded

When attempting to mount Virtual Media on a iDRAC6 IP KVM session I get the following error: I'm using Ubuntu 9.04 and: $ javaws -version Java(TM) Web Start 1.6.0_16 $ uname -a Linux aud22419-linux 2.6.28-15-generic #51-Ubuntu SMP Mon Aug 31 13:39:06 UTC 2009 x86_64 GNU/Linux $ firefox -version Mozilla Firefox 3.0.14, Copyright (c) 1998 - 2009 mozilla.org On Windows + IE it (unsurprisingly) works. I've just gotten off the phone with the Dell tech support and I was told it is known to work on Linux + Firefox, albeit Ubuntu is not supported (by Dell, that is). Has anyone out there managed to mount virtual media in the same scenario?
Post a Comment
Read more

hp proliant - Smart Array P822 with HBA Mode?

We get an HP DL360 G8 with an Smart Array P822 controller. On that controller will come a HP StorageWorks D2700 . Does anybody know, that it is possible to run the Smart Array P822 in HBA mode? I found only information about the P410i, who can run HBA. If this is not supported, what you think about the LSI 9207-8e controller? Will this fit good in that setup? The Hardware we get is used but all original from HP. The StorageWorks has 25 x 900 GB SAS 10K disks. Because the disks are not new I would like to use only 22 for raid6, and the rest for spare (I need to see if the disk count is optimal or not for zfs). It would be nice if I'm not stick to SAS in future. As OS I would like to install debian stretch with zfs 0.71 as file system and software raid. I have see that hp has an page for debian to. I would like to use hba mode because it is recommend, that zfs know at most as possible about the disk, and I'm independent from the raid controller. For us zfs have many benefits,
Post a Comment
Read more

apache 2.2 - Server Potentially Compromised -- c99madshell

So, low and behold, a legacy site we've been hosting for a client had a version of FCKEditor that allowed someone to upload the dreaded c99madshell exploit onto our web host. I'm not a big security buff -- frankly I'm just a dev currently responsible for S/A duties due to a loss of personnel. Accordingly, I'd love any help you server-faulters could provide in assessing the damage from the exploit. To give you a bit of information: The file was uploaded into a directory within the webroot, "/_img/fck_uploads/File/". The Apache user and group are restricted such that they can't log in and don't have permissions outside of the directory from which we serve sites. All the files had 770 permissions (user rwx, group rwx, other none) -- something I wanted to fix but was told to hold off on as it wasn't "high priority" (hopefully this changes that). So it seems the hackers could've easily executed the script. Now I wasn't able
Post a Comment
Read more