[CentOS] Information Week: RHEL 7 released today

Thu Jun 12 17:27:24 UTC 2014
Warren Young <warren at etr-usa.com>

On 6/11/2014 07:11, Timothy Murphy wrote:
> Does XFS have any advantages over ext4 for normal users, eg with laptops?

If you graph machine size -- in whatever dimension you like -- vs number 
deployed, I think you'd find all laptops over on the left side of the 
CentOS deployment curve.  I'd expect that curve to be a skewed bell, 
with a long tail of huge servers over on the right side.

ext* came up from the consumer world at the same time that XFS was 
coming down from the Big Iron world.  The gap between them has thus been 
shrinking, so that as implemented in EL7, ext4 has an awful lot of 
overlap with XFS in terms of features and capabilities.

XFS still offers a lot more upside, and is more appropriate for the 
server systems that CentOS will most often be used on.  It is a more 
sensible default, being the right answer for the biggest subset of the 
CentOS user base.

Since you're over there on the left side of the curve, you may well 
decide that ext4 still makes more sense for you.

That said, there really isn't anything about laptop use that argues 
*against* using XFS.  It isn't a perfect filesystem, but then, neither 
is ext4.

> I've only seen it touted for machines with enormous disks, 200TB plus.

ext4 in EL7 only goes to 50 TiB, whereas XFS is effectively 
unlimited[*].  Red Hat will only support up to 500 TiB with XFS in EL7, 
but I suspect it isn't due to any XFS implementation limit, but just a 
more professional way for them to say "Don't be silly."

[*] The absolute XFS filesystem size limit is about 8 million terabytes, 
which requires about 500 cubic meters of the densest HDDs available 
today.  You'd need 13 standard shipping containers (1 TEU) to transport 
them all, without any space for packing material.  If we add 20% more 
disks for a reasonable level of redundancy and put them in 24-disk 4U 
chassis and mount those chassis in full-size racks, we need about half a 
soccer field of floor space -- something like ~4000 m^2 -- after 
accounting for walking space, network switches, redundant power, and 
whatnot to run it all.  It's so many HDDs that you'd need four or five 
full-time employees in 3 shifts to respond to drive failures fast enough 
to keep an 8 EiB array from falling over due to insufficient redundancy. 
  You simply wouldn't make a single XFS filesystem that big today, so 
QED: effectively unlimited.