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Re: Deb10 installer can't install grub

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On 05/03/2021 09:25, Anssi Saari wrote:
> Greg Wooledge <greg@wooledge.org> writes:
>
>> tomas@tuxteam.de (tomas@tuxteam.de) wrote:
>>>> 1x 4TB, single drive,          3.7 TB,  w=108MB/s , rw=50MB/s  , r=204MB/s 
>>>> 2x 4TB, mirror (raid1),        3.7 TB,  w=106MB/s , rw=50MB/s , r=488MB/s 
>>> Thanks. Real data :)
>>>
>>> The doubling in read throughput is somewhat surprising to me. Some
>>> learning to do, it seems.
>> There are two copies of everything.  So, if you need to read a big
>> file, you can read half of it from disk 1 and the other half from disk 2,
>> roughly simultaneously.
> I have a vague memory of reading once that mdraid doesn't stripe reads
> to a single file. I.e. with raid1 you get the double speed if you read
> different files (or different parts of disk) but reading a single file,
> no.
RAID won't know what's a file or not. It works below the file system
layer, so only concerns itself with blocks. For any particular block, a
RAID1 array has N copies of that block to read from. It makes no sense
to read all of those copies - imagine if you were really paranoid and
had a 10-disk RAID array. Instead, the driver will choose one of the
constituent drives and read the block from that drive. So, if your file
is small, then yes, you won't see any performance benefit. But if your
file is larger than a block, or if you want to access more than one file
at once, then RAID can read the second block from a different drive.
Remember that  the I in RAID stands for Inexpensive. RAID assumes that
the disk is slow, the bus is faster and the applications are impatient  :)
>
> So is this different in zfs? I guess I could test this myself. The way
> Bonnie++ was used for those results above is definitely parallel.
ZFS will work in much the same manner, except when performing a "scrub".
During a scrub, all copies of all blocks are read and compared. If a
block differs across the mirrors, then ZFS has a decision to make: if
there are more identical copies than different copies, ZFS assumes that
the identical copies are good (hence why having a three-way mirror is
recommended). Alternatively, ZFS uses checksums on stored data. If the
block doesn't match the checksum, then ZFS can also recover that data.
More details here
https://blogs.oracle.com/bonwick/zfs-end-to-end-data-integrity
>

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Deb10 installer can't install grub Dave Sherohman <dave@sherohman.org> - 2021-03-02 13:30 +0100
  Re: Deb10 installer can't install grub Dan Ritter <dsr@randomstring.org> - 2021-03-02 14:00 +0100
    Re: Deb10 installer can't install grub The Wanderer <wanderer@fastmail.fm> - 2021-03-02 14:30 +0100
      Re: Deb10 installer can't install grub Dan Ritter <dsr@randomstring.org> - 2021-03-02 16:00 +0100
        Re: Deb10 installer can't install grub The Wanderer <wanderer@fastmail.fm> - 2021-03-02 16:00 +0100
        Re: Deb10 installer can't install grub Charles Curley <charlescurley@charlescurley.com> - 2021-03-02 17:20 +0100
    Re: Deb10 installer can't install grub Dave Sherohman <dave@sherohman.org> - 2021-03-02 15:10 +0100
      Re: Deb10 installer can't install grub The Wanderer <wanderer@fastmail.fm> - 2021-03-02 15:20 +0100
        Re: Deb10 installer can't install grub The Wanderer <wanderer@fastmail.fm> - 2021-03-02 15:30 +0100
          Re: Deb10 installer can't install grub Dave Sherohman <dave@sherohman.org> - 2021-03-02 15:40 +0100
        Re: Deb10 installer can't install grub Dave Sherohman <dave@sherohman.org> - 2021-03-02 15:30 +0100
    Re: Deb10 installer can't install grub Felix Miata <mrmazda@earthlink.net> - 2021-03-02 20:10 +0100
      Re: Deb10 installer can't install grub Andrei POPESCU <andreimpopescu@gmail.com> - 2021-03-03 17:00 +0100
        Re: Deb10 installer can't install grub Felix Miata <mrmazda@earthlink.net> - 2021-03-03 23:20 +0100
          Re: Deb10 installer can't install grub Dan Ritter <dsr@randomstring.org> - 2021-03-03 23:50 +0100
            Re: Deb10 installer can't install grub <tomas@tuxteam.de> - 2021-03-04 10:10 +0100
              Re: Deb10 installer can't install grub Greg Wooledge <greg@wooledge.org> - 2021-03-04 14:20 +0100
                Re: Deb10 installer can't install grub <tomas@tuxteam.de> - 2021-03-04 14:30 +0100
                Re: Deb10 installer can't install grub Anssi Saari <as@sci.fi> - 2021-03-05 10:30 +0100
                Re: Deb10 installer can't install grub Darac Marjal <mailinglist@darac.org.uk> - 2021-03-05 11:10 +0100
                Re: Deb10 installer can't install grub Andy Smith <andy@strugglers.net> - 2021-03-05 13:00 +0100
          Re: Deb10 installer can't install grub <tomas@tuxteam.de> - 2021-03-04 10:10 +0100
          Re: Deb10 installer can't install grub Andrei POPESCU <andreimpopescu@gmail.com> - 2021-03-05 14:50 +0100
  Re: Deb10 installer can't install grub "Andrew M.A. Cater" <amacater@einval.com> - 2021-03-02 22:00 +0100
  Re: Deb10 installer can't install grub Dave Sherohman <dave@sherohman.org> - 2021-03-03 10:00 +0100
    SOLVED - Re: Deb10 installer can't install grub Dave Sherohman <dave@sherohman.org> - 2021-03-03 12:30 +0100
      Re: SOLVED - Re: Deb10 installer can't install grub Marc Auslander <marcausl@gmail.com> - 2021-03-03 16:50 +0100
        Re: SOLVED - Re: Deb10 installer can't install grub Dave Sherohman <dave@sherohman.org> - 2021-03-07 14:10 +0100
          Re: SOLVED - Re: Deb10 installer can't install grub Nicholas Geovanis <nickgeovanis@gmail.com> - 2021-03-07 15:10 +0100
    Re: Deb10 installer can't install grub Anssi Saari <as@sci.fi> - 2021-03-04 10:10 +0100

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