Re: Raid-10 mount at startup always has problem

[Bill Davidsen <davidsen@tmr.com>]

Luca Berra wrote:
> On Sun, Oct 28, 2007 at 08:21:34PM -0400, Bill Davidsen wrote:
>>> Because you didn't stripe align the partition, your bad.
>>>   
>> Align to /what/ stripe? Hardware (CHS is fiction), software (of the RAID 
> the real stripe (track) size of the storage, you must read the manual
> and/or bug technical support for that info.

That's my point, there *is* no "real stripe (track) size of the storage" 
because modern drives use zone bit recording, and sectors per track 
depends on track, and changes within a partition. See
  http://www.dewassoc.com/kbase/hard_drives/hard_disk_sector_structures.htm
  http://www.storagereview.com/guide2000/ref/hdd/op/mediaTracks.html
>> you're about to create), or ??? I don't notice my FC6 or FC7 install 
>> programs using any special partition location to start, I have only 
>> run (tried to run) FC8-test3 for the live CD, so I can't say what it 
>> might do. CentOS4 didn't do anything obvious, either, so unless I 
>> really misunderstand your position at redhat, that would be your 
>> bad.  ;-)
>>
>> If you mean start a partition on a pseudo-CHS boundary, fdisk seems 
>> to use what it thinks are cylinders for that.
> Yes, fdisk will create partition at sector 63 (due to CHS being 
> braindead,
> other than fictional: 63 sectors-per-track)
> most arrays use 64 or 128 spt, and array cache are aligned accordingly.
> So 63 is almost always the wrong choice.

As the above links show, there's no right choice.
>
> for the default choice you must consider what spt your array uses, iirc
> (this is from memory, so double check these figures)
> IBM 64 spt (i think)
> EMC DMX 64
> EMC CX 128???
> HDS (and HP XP) except OPEN-V 96
> HDS (and HP XP) OPEN-V 128
> HP EVA 4/6/8 with XCS 5.x state that no alignment is needed even if i
> never found a technical explanation about that.
> previous HP EVA versions did (maybe 64).
> you might then want to consider how data is laid out on the storage, but
> i believe the storage cache is enough to deal with that issue.
>
> Please note that "0" is always well aligned.
>
> Note to people who is now wondering WTH i am talking about.
>
> consider a storage with 64 spt, an io size of 4k and partition starting
> at sector 63.
> first io request will require two ios from the storage (1 for sector 63,
> and one for sectors 64 to 70)
> the next 7 io (71-78,79-86,97-94,95-102,103-110,111-118,119-126) will be
> on the same track
> the 8th will again require to be split, and so on.
> this causes the storage to do 1 unnecessary io every 8. YMMV.
No one makes drives with fixed spt any more. Your assumptions are a 
decade out of date.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979