[illumos-Developer] illumos bug/rfe 453

[Deano]

Hi,
I believe that the IDEMA group decided that SATA would emulate only until
around 2012 (when OS support is complete), whereas SAS can be 512 or 4KiB
but I've yet to see a 4KiB native drive, but we should see them soon (or
they are around). Both the SCSI and ATA protocol drivers in illumos already
support the physical exponent read (how many logical block per physical
block), so in theory that should just work out the box when we get a true
4KiB reporting drive.

sd.conf already has a static drive identification/workaround format and
system, so we will just add a field/bit to that to indicate 4KiB physical
size is required. There is already a similar field for SSDs, it may be
possible to co-opt that to cover both SSD and spindle 4KiB drives but that
will be need looking at.

Any info from arc would be useful.

Thanks,
Deano
Deano at cloudpixies.com

-----Original Message-----
From: wessels [mailto:wessels147 at gmail.com] 
Sent: 24 January 2011 17:39
To: Developer at lists.illumos.org
Subject: Re: [illumos-Developer] illumos bug/rfe 453

Hi,

indeed zfs isn't relevant here, I meant zpool. And yes zpool can
handle larger sector sizes already. The size is stored in the ashift
property upon creation. Patched zpool versions do exist which override
ashift and fix it to 12bits (4K). I've read the various topics and
benchmarks regarding the WD20EARS for example.
I've also read the reports of succesfull use of mixed sector sizes in
zpool's. But I didn't study the code so don't know for sure if the
zpool programmers had the intention to support different sector sizes
in one zpool. That's why I mentioned the cases concerning mixed
devices, eg harddisks 512bytes and L2ARC ssd with reported 512bytes
but would benefit greatly when aligned 4K i/o's would be done against
it.
Are you aware of any device SAS or SATA which actually reports 4K
sectors? That would make testing more interesting. I was hoping that
the new hitachi drives would report 4K, but they don't.
What format do you suggest for the SD tunable list ? Something in the
form of a list of id's (vendor, model, firmware etc) and per model a
requested size? A different scheme would be per device (port). But
that require much more maintenance.
Regarding the test suite. That would be very interesting. A SD driver
reporting 4K and a test suite which check's if the data is nicely
aligned on this 512bytes disk. I wanted to check this once on a
windows system and had to boot some linux toolbox to read the disk
realiable.
If you want I can lookup when the other two arc's were integrated. I
don't have the new Solaris 11 SXCE or whatever it's called which would
be interesting to use as reference for PSARC/2010/296

Regards

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