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Re: Raid 1

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On 2021-01-23 07:01, mick crane wrote:
> On 2021-01-23 12:20, Andrei POPESCU wrote:
>> On Vi, 22 ian 21, 22:26:46, mick crane wrote:
>>> hello,
>>> I want to tidy things up as suggested.
>>> Have one old PC that I'll put 2 disks in and tidy everything up so 
>>> what's
>>> scattered about is on the running disks and this new/old one is just 
>>> backup
>>> for them.
>>> Can I assume that Debian installer in some expert mode will sort out the
>>> raid or do I need to install to one disk and then mirror it manually 
>>> before
>>> invoking the raid thing ?
>>
>> The "raid thing" is a separate layer below the partitions and file
>> systems.
>>
>> Technically it is possible to create the mirror with just one device (I
>> believe mdadm calls this "degraded"), partition the md mirror device,
>> install, copy data to it, etc., add the second device later and let md
>> synchronize the two drives.
>>
>> Because Linux RAID is a separate layer with no knowledge of the data
>> "above" it has to copy every single bit to the other drive as well
>> (similar to a dd device-to-device copy), regardless if actually needed
>> or not.
>>
>> If you are really strapped for space and must do this ZFS can do it much
>> more efficiently, because it controls the entire "stack" and knows
>> exactly which blocks to copy (besides many other advantages over Linux
>> RAID).
>>
>> Unfortunately ZFS is slightly more complicated from the packaging side,
>> and installing Debian on a ZFS root is difficult.
>>
>> It still makes an excelent choice to manage your storage drives,
>> especially on a stable system, where there is less hassle with the dkms
>> module and it's amazingly simple to use once you familiarise yourself
>> with the basics.
>>
>> Kind regards,
>> Andrei
> 
> Sigh, OK I take advice and have a go.
> Really I just want to get on and do some drawings or something but I 
> think I'll thank myself later if I get proper backup in place.
> If after having a quick look am I understanding anything?
> Partition and install minimal Debian with no X or anything on just one 
> disk.
> install headers and zfs-utils.
> Add other disk and then what ? To make it a mirror pool (like raid1) 
> does zfs take care of the partitions.
> Do I want to delete all partitions on other disk first or make like for 
> like partitions?
> 
> If that's done and I've made a zpool called  "backup" from then on the 
> ZFS is nothing to do with the kernel ?
> I ask kernel make a directory "my_pc1"
> then
> "zfs create -o mountpoint=/my_pc1 backup/my_pc1"
> 
> I ask kernel make a directory "my_pc2"
> then
> "zfs create -o mountpoint=/my_pc2 backup/my_pc2"
> 
> So then I can copy files from other PC (pc1) to 
> "my_backup_pc/backup/my_pc1" and ZFS mirrors the data to other disk in 
> pool ?
> 
> If that's how it works I'll just need something on the backup_pc and the 
> other PCs to automate the backing up.
> Is that backup Ninja or something ?


RAID protects against storage device sectors going bad and against 
entire storage devices going bad -- e.g. hard disk drives, solid state 
drives, etc..


Backups protect against filesystem contents going bad -- e.g. files, 
directories, metadata, etc..


While putting an operating system and backups within a single RAID can 
be done, this will complicate creation of a ZFS pool and will complicate 
disaster preparedness/ recovery procedures.  The following instructions 
assume your OS is on one device and that you will dedicate two HDD's to ZFS.


See "Creating a Mirrored Storage Pool":

https://docs.oracle.com/cd/E19253-01/819-5461/gaynr/index.html


The above URL is good for concepts, but the virtual device names 
('c1d0', 'c2d0') are for Solaris.  For Debian, you will want to 
zero-fill both HDD's with dd(1) and then create the pool with zpool(8) 
using device identity nodes:

     /dev/disk/by-id/ata-...


Be extremely careful that you specify the correct devices!


ZFS will mark the drives and create a ZFS pool named 'tank' mounted at 
'/tank'.  Note the parallel namespaces -- 'tank'is ZFS namespace and has 
no leading slash, while '/tank' is a Unix absolute path.


'/tank' is a ZFS filesystem that can do everything a normal Unix 
directory can do.  So, you could create a directory for backups and 
create directories for specific machines:

# mkdir /tank/backup

# mkdir /tank/backup/pc1

# mkdir /tank/backup/pc2


Or, you could create a ZFS filesystem for backups and create ZFS 
filesystems for specific machines:

# zfs create tank/backup

# zfs create tank/backup/pc1

# zfs create tank/backup/pc2


Both will give you directories that you can put your backups into using 
whatever tools you choose, but the latter will give you additional ZFS 
capabilities.


David

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Thread

Raid 1 mick crane <mick.crane@gmail.com> - 2021-01-22 23:30 +0100
  Re: Raid 1 Linux-Fan <Ma_Sys.ma@web.de> - 2021-01-23 00:10 +0100
  Re: Raid 1 David Christensen <dpchrist@holgerdanske.com> - 2021-01-23 00:20 +0100
  Re: Raid 1 David Christensen <dpchrist@holgerdanske.com> - 2021-01-23 00:20 +0100
  Re: Raid 1 Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-23 13:30 +0100
    Re: Raid 1 Linux-Fan <Ma_Sys.ma@web.de> - 2021-01-23 18:20 +0100
      Re: Raid 1 Linux-Fan <Ma_Sys.ma@web.de> - 2021-01-23 19:00 +0100
        Re: Raid 1 Pankaj Jangid <pankaj@codeisgreat.org> - 2021-01-25 07:00 +0100
          Re: Raid 1 Andy Smith <andy@strugglers.net> - 2021-01-25 08:20 +0100
            Re: Raid 1 Linux-Fan <Ma_Sys.ma@web.de> - 2021-01-25 12:10 +0100
              Re: Raid 1 Pankaj Jangid <pankaj@codeisgreat.org> - 2021-01-25 13:50 +0100
    Re: Raid 1 David Christensen <dpchrist@holgerdanske.com> - 2021-01-23 23:10 +0100
      Re: Raid 1 Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-24 18:40 +0100
        Re: Raid 1 Linux-Fan <Ma_Sys.ma@web.de> - 2021-01-24 23:30 +0100
          Re: Raid 1 Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-25 07:40 +0100
      Re: Raid 1 Andy Smith <andy@strugglers.net> - 2021-01-24 19:00 +0100
        Re: Raid 1 Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-24 21:20 +0100
      Re: Raid 1 David Christensen <dpchrist@holgerdanske.com> - 2021-01-24 21:20 +0100
        Re: Raid 1 deloptes <deloptes@gmail.com> - 2021-01-25 09:50 +0100
        Re: Raid 1 David Christensen <dpchrist@holgerdanske.com> - 2021-01-25 19:00 +0100

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