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

[Peter Milesson <miles@xxxxxxxx>]

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. Links below. It's mostly about XenServer, but I 
assume it applies to Xen also. 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.
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.
https://community.spiceworks.com/topic/1457343-best-possible-way-to-configure-raid-with-4kn-drives
https://discussions.citrix.com/topic/383676-is-xenserver-7-an-advanced-format-512e-or-4kn-aware-os/
https://filers.blogspot.com/2018/12/citrix-xenserver-support-for-4k-sector.html

Best regards,

Peter

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