Date: Sat, 18 Aug 2007 04:44:24 +0200 From: Ivan Voras <ivoras@fer.hr> To: freebsd-stable@freebsd.org Subject: Re: large RAID volume partition strategy Message-ID: <fa5men$v5r$1@sea.gmane.org> In-Reply-To: <EED39309-A95F-4A2D-8E35-C1650A55E482@khera.org> References: <31BB09D7-B58A-47AC-8DD1-6BB8141170D8@khera.org> <fa5b4v$8e5$1@sea.gmane.org> <EED39309-A95F-4A2D-8E35-C1650A55E482@khera.org>
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Vivek Khera wrote:
> My only fear of this is that once this system is in production, that's
> pretty much it. Maintenance windows are about 1 year apart, usually
> longer.
Others will have to comment about that. I have only one 7-CURRENT in
production (because of ZFS) and I had only one panic (in ZFS). But this
machine is not heavily utilized.
>> When you get there, you'll need to create 1 small RAID volume (<=3D 1 =
GB)
>> from which to boot (and probably use it for root) and use the rest for=
>> whatever your choice is (doesn't really matter at this point). This is=
>> because you can't have fdisk or bsdlabel partitions larger than 2 TB a=
nd
>> you can't boot from GPT.
>=20
> So what your saying here is that I can't do either my option 1 or 2, bu=
t
> have to create smaller volumes exported as individual drives? Or just
> that I can't do 1, because my case 2 I could make three 2Tb fdisk slice=
s
> which bsdlabel can then partition?
fdisk and bsdlabels both have a limit: because of the way they store the
data about the disk space they span, they can't store values that
reference space > 2 TB. In particular, every partition must start at an
offset <=3D 2 TB, and cannot be larger than 2 TB.
In theory, the maximum you could do in "normal" (read on) circumstances
is have a 4 TB volume partitioned into two 2 TB slices/partitions, and
that's it. In practice, you can't usefully partition drives larger than
2 TB at all.
There's one (also theoretical... I doubt anyone has tried it) way out of
it: simulate a device with larger sector size through gnop(8). For
example, if you use a 1 KB sector size you'll double all the limits (at
least for bsdlabel, I think fdisk is stuck in 512-byte sectors) to 4 TB,
for 4 KB sectors, to 16 TB). I know from experience that UFS can handle
sectors up to 8 KB, other file systems might not.
(ref: sys/disklabel.h:
struct partition { /* the partition table */
u_int32_t p_size; /* number of sectors in partition=
*/
u_int32_t p_offset; /* starting sector */
u_int32_t p_fsize; /* filesystem basic fragment size=
*/
u_int8_t p_fstype; /* filesystem type, see below */
u_int8_t p_frag; /* filesystem fragments per block=
*/
u_int16_t p_cpg; /* filesystem cylinders per group=
*/
} d_partitions[MAXPARTITIONS]; /* actually may be more */
)
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