Re: [Xen-users] Xen hypervisor and HDDs with 4K sectors

[Peter Milesson <miles@xxxxxxxx>]

On 2019-05-28 15:39, J. Roeleveld wrote:
> On Tuesday, May 28, 2019 12:05:31 PM CEST Peter Milesson wrote:
> > On 2019-05-28 10:40, J. Roeleveld wrote:
> > > Peter,
> > >
> > > On zondag 26 mei 2019 19:31:22 CEST Peter Milesson wrote:
> > > > On 2019-05-26 15:28, Simon Hobson wrote:
> > > > > > I want to use the most modern hardware possible, and in line with that,
> > > > > > I
> > > > > > would like to have the option to use HDD (or SSD) drives with 4K
> > > > > > sectors
> > > > > > through a hardware RAID controller.
> > > I have since switched to using ZFS for the storage layer, but on my
> > > previous setup, I was using Xen, LVM and 4K sector disks with a hardware
> > > raid controller. Never experienced any issues related to the disks being
> > > 4K.
> > >
> > > As recent tools all tend to default to aligning on 4K regardless, I didn't
> > > even encounter any bad performance either.
> > >
> > > > > > I have been searching information about Xen and support for drives with
> > > > > > 4K sectors, but I haven't seen much information on the subject. I would
> > > > > > be sincerely "dissappointed" if I purchase a new server for 10000+ USD,
> > > > > > only to discover it to be utter useless.>
> > > I buy them in Euros, but would also be annoyed if the server would be less
> > > then 1000 USD or EUR.
> > >
> > > > > It shouldn't matter.
> > > > > As long as the hardware is supported in Xen/Dom0, and you partition on
> > > > > 4k
> > > > > boundaries, then the guests should be isolated from the underlying
> > > > > details. Obviously it would be a good idea to also partition any virtual
> > > > > drives on 4k boundaries (if partitioning in the guests).
> > > This was my experience as well, but would like to add that partitioning
> > > tools tend to default to 4K in any case.
> > >
> > > > Hi Simon,
> > > >
> > > > Thanks for your input. That's the point. I have seen a few posts that
> > > > the advanced disk format using 4K sectors is not compatible with Xen.
> > > Can you provide links? As I am curious on this.
> > >
> > > --
> > > Joost
> > Hi Joost,
> >
> > Thanks for your input.
> You're welcome.
>
> > Links below. It's mostly about XenServer, but I
> > assume it applies to Xen also.
> Not necessarily, XenServer is OS+Xen.
> I use Gentoo with Xen.
>
> > There doesn't seem to be many links much
> > later than 2016. It either implies that almost everything is 4K today,
> > or the server manufacturers still clinging to 512 bytes, with the 512e
> > disks some kind of strange animal in the jungle. I read the manual for
> > HPE Smart Array Administrator, and 512e drives where mentioned in a way,
> > that just muddles things even more.
> I haven't used HPA SAA myself, but if that doesn't support 4K drives, you need
> to find something to replace it with.
>
> > At least for desktop PCs, there seems to be a mix of HDDs available
> > (512, 512e, and 4K). I migrated a SATA HDD to a SSD today, and CentOS
> > reported the HDD to be of type 512e (512 bytes logical/4096 physical),
> > while the (brand new 1TB SSD) was a pure 512 drive. So much for the
> > advanced format. Anyway, the migration was successful.
> My current server uses 512n SAS drives because I couldn't find decent 4kn
> drives. I prefer drives to be honest about what they report to the OS. On the
> previous system, I had no choice as the only affordable disks were all 512e
> (4K, but pretending to be 512) drives.
>
> > https://community.spiceworks.com/topic/1457343-best-possible-way-to-configur
> > e-raid-with-4kn-drives
> Seems to be an issue with the hardware raid device, not the OS or Xen.
>
> > https://discussions.citrix.com/topic/383676-is-xenserver-7-an-advanced-form
> > at-512e-or-4kn-aware-os/
> "No official support, but does seem to work"
>
> > https://filers.blogspot.com/2018/12/citrix-xenserver-support-for-4k-sector.
> > html
> A single comment with no real value. If this were on an official (either Xen
> or Citrix) website, I would consider it. But when found on blogspot with no
> explanation, I would ignore it.
Hi Joost,

I got hold of the newest HDD list from HPE. Most drives are 512n, with a 
few 512e drives. HPE does not offer 4kn drives. If I get a decent quote 
on a new server with SSD drives, I'll jump onto that train. 512n, or 4kn 
should more or less be irrelevant with SSD disks, as there are no 
mechanics involved.
I wish you a nice day,

Peter



_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-users