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Re: Questions about XFS

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: Questions about XFS
From: harryxiyou <harryxiyou@xxxxxxxxx>
Date: Sat, 26 Oct 2013 00:24:07 +0800
Cc: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
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On Fri, Oct 25, 2013 at 10:57 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote:
> well, yes and no.  It supports the "realtime subvolume" which is
> not really technically "realtime."  It does have a more deterministic
> allocator, but it doesn't have GRIO (Guaranteed Realtime I/O) like
> IRIX does.

Hmmm..., however, I find the manual of mkfs.xfs tell me as follows.

       -r realtime_section_options
              These options specify the location, size, and  other
parameters  of  the
              real-time  section  of the filesystem. The valid

                          This is used to specify the device which
should  contain  the
                          real-time  section of the filesystem.  The
suboption value is
                          the name of a block device.

                          This is used to specify the size of the
blocks in  the  real-
                          time section of the filesystem. This value
must be a multiple
                          of the filesystem block size. The minimum
allowed size is the
                          filesystem  block  size  or  4 KiB
(whichever is larger); the
                          default size is the stripe width for striped
 volumes  or  64
                          KiB  for  non-striped  volumes; the maximum
allowed size is 1
                          GiB. The real-time extent size should be
carefully chosen  to
                          match the parameters of the physical media used.

                          This  is  used  to specify the size of the
real-time section.
                          This suboption is only needed if the
real-time section of the
                          filesystem should occupy less space than the
size of the par?
                          tition or logical volume containing the section.

After I run "mkfs.xfs -r rtdev=/dev/sda3 extsize=64K", I wonder what the
differences between '/dev/sda3' and '/dev/sda2' (/dev/sda2 is common XFS or
EXT2). The differences are as follows, right?

1, I/O speed of real-time '/dev/sda3' is faster?
2, The performance of '/dev/sda3â is better?

Anything else?

Weiwei  Jia (Harry Wei)

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