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Thread: partition/volume

  1. #31

    Default Re: partition/volume

    Quote Originally Posted by dcurtisfra View Post
    Correct – the Btrfs RAID will contained striped user files (only one copy visible to the users) but, the Btrfs Metadata will held per SSD (one copy per SSD).
    Ah, this is the deep magic that wasn't obvious in any of the Btrfs lit I dug into - while I suppose obvious to some, just not me.So you're saying that although the Btrfs RAID (two SSD's) will "appear" to the OS as a single "device" with multiple partitions ("subvolumes"), Btrfs is smart enough to know that it's 2 devices in reality.

    So there are 4 options:
    1. mkfs.btrfs -m raid0 -d raid0
    2. mkfs.btrfs -m raid0 -d raid1
    3. mkfs.btrfs -m raid1 -d raid0 (the one given in the example on a Btrfs wiki page)
    "By default, metadata will be mirrored across two devices and data will be striped across all of the devices present."
    (really complicated)

    4. mkfs.btrfs -m raid1 -d raid1

    Choosing -m raid0 appears to "stripe the metadata." One could also choose -d raid1 to "mirror the data."
    I suppose this could be tested... "Btrfs can add and remove devices online, and freely convert between RAID levels after the FS has been created."

    A bit dated (2014) benchmark: (it looks like raid0 is quite preferred for speed... but another source says raid1 is the most heavily-tested Btrfs raid level)
    https://www.phoronix.com/scan.php?pa..._ssdraid&num=3

  2. #32

    Default Re: partition/volume

    So I currently have two partitions I need to move over to a new Btrfs system. I'll do a bare metal install of Opensuse on the new Btrfs system. Besides the new subvolumes this will create (/ and /home, etc.) I need to move these partitions over to the new Btrfs system. One is a drive with a single primary data partition on it (sdb), and the other is a data partition on sda (which also contains / and /home).

    On the new system, I guess I just create subvolumes of the same names as those two partitions, copy the data, and Linux will treat them the same as before?

    (Asking b/c "better safe than sorry")

  3. #33
    Join Date
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    Default Re: partition/volume

    Quote Originally Posted by pattiM View Post
    On the new system, I guess I just create subvolumes of the same names as those two partitions, copy the data, and Linux will treat them the same as before?
    RAID is “normally” used only for user data partitions and, the (system) /srv partition –
    • Whether or not the system partitions ( / – /tmp – /var – /boot «especially in the UEFI case» – /mnt ) should be part of a RAID is a moot point …
    • My personal view is, that the system files should not be part of a RAID …

  4. #34

    Default Re: partition/volume SSD BtrFS btrfs

    Well, using two SSD's seems to have worked with the default BtrFS configuration (striped data, mirrored metadata).

    How I set this up: (assuming two identical SSD's)
    =============
    Start 15.2 installer

    At the partitioning, select expert partitioner based on *suggested* configuration
    - Yast will suggest setting up only on sda
    - this will make sure that the boot system partitions (grub) are set up properly

    Go to Btrfs in left-hand navigation bar

    Add devices to the Btrfs partition (both sda and sdb - the two SSD's)

    I also added the fstab option of compress=zlib

    Default raid should be correct

    ...then just continue with a normal setup. Both SSD's will be combined into a single BtrFS filesystem with mirrored metadata and striped data.

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