[CentOS] Information Week: RHEL 7 released today
Warren Young
warren at etr-usa.com
Thu Jun 12 17:27:24 UTC 2014
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.
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