How do I tell if my partition is aligned for a 64k/RAID-6?

How do I tell if my partition is aligned for a 64k/RAID-6?

[Justin Piszcz]

Output:

===============================================================================

p34:~# parted /dev/sda print unit s print unit chs print
Model: AMCC 9650SE-16M DISK (scsi)
Disk /dev/sda: 13.0TB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name  Flags
  1      17.4kB  13.0TB  13.0TB  xfs

Model: AMCC 9650SE-16M DISK (scsi)
Disk /dev/sda: 25390350336s
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start  End           Size          File system  Name  Flags
  1      34s    25390350302s  25390350269s  xfs

Model: AMCC 9650SE-16M DISK (scsi)
Disk /dev/sda: 1580476,53,56
Sector size (logical/physical): 512B/512B
BIOS cylinder,head,sector geometry: 1580476,255,63.  Each cylinder is 8225kB.
Partition Table: gpt

Number  Start   End            File system  Name  Flags
  1      0,0,34  1580476,53,23  xfs

p34:~#

===============================================================================

I created a partition from 0Gb to 13T on the following LUN, but how do I 
verify this is aligned to the (hardware) 64KiB raid-6 array?

Unit  UnitType  Status         %RCmpl  %V/I/M  Stripe  Size(GB)  Cache  AVrfy
------------------------------------------------------------------------------
u0    RAID-6    OK             -       -       64K     12107.1   ON     ON

===============================================================================

p34:~# xfs_info /dev/sda1
meta-data=/dev/sda1              isize=256    agcount=12, agsize=268435455 
blks
          =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=3173793783, imaxpct=5
          =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096
log      =internal               bsize=4096   blocks=32768, version=2
          =                       sectsz=512   sunit=0 blks, lazy-count=0
realtime =none                   extsz=4096   blocks=0, rtextents=0

===============================================================================

I am not worried about the filesystem as the defaults usually get it right 
but with parted, this is the first time I had to use it for home use and 
with RAID-6 I am noticing slower performance with 15 disks (1 is a spare) 
in RAID-6 (albeit slower 7200 ones, RE3s) than I was getting with 10 
raptor150s in RAID-6 (but I had used fdisk there).

Justin.

Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[Justin Piszcz]

On Thu, 25 Dec 2008, Justin Piszcz wrote:

> Output:
>
> ===============================================================================
>
> p34:~# parted /dev/sda print unit s print unit chs print
> Model: AMCC 9650SE-16M DISK (scsi)
> Disk /dev/sda: 13.0TB
> Sector size (logical/physical): 512B/512B
> Partition Table: gpt
>
> Number  Start   End     Size    File system  Name  Flags
> 1      17.4kB  13.0TB  13.0TB  xfs
>
> Model: AMCC 9650SE-16M DISK (scsi)
> Disk /dev/sda: 25390350336s
> Sector size (logical/physical): 512B/512B
> Partition Table: gpt
>
> Number  Start  End           Size          File system  Name  Flags
> 1      34s    25390350302s  25390350269s  xfs
>
> Model: AMCC 9650SE-16M DISK (scsi)
> Disk /dev/sda: 1580476,53,56
> Sector size (logical/physical): 512B/512B
> BIOS cylinder,head,sector geometry: 1580476,255,63.  Each cylinder is 8225kB.
> Partition Table: gpt
>
> Number  Start   End            File system  Name  Flags
> 1      0,0,34  1580476,53,23  xfs
>
> p34:~#
>
> ===============================================================================
>
> I created a partition from 0Gb to 13T on the following LUN, but how do I 
> verify this is aligned to the (hardware) 64KiB raid-6 array?
>
> Unit  UnitType  Status         %RCmpl  %V/I/M  Stripe  Size(GB)  Cache  AVrfy
> ------------------------------------------------------------------------------
> u0    RAID-6    OK             -       -       64K     12107.1   ON     ON
>
> ===============================================================================
>
> p34:~# xfs_info /dev/sda1
> meta-data=/dev/sda1              isize=256    agcount=12, agsize=268435455 
> blks
>         =                       sectsz=512   attr=2
> data     =                       bsize=4096   blocks=3173793783, imaxpct=5
>         =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096
> log      =internal               bsize=4096   blocks=32768, version=2
>         =                       sectsz=512   sunit=0 blks, lazy-count=0
> realtime =none                   extsz=4096   blocks=0, rtextents=0
>
> ===============================================================================
>
> I am not worried about the filesystem as the defaults usually get it right 
> but with parted, this is the first time I had to use it for home use and with 
> RAID-6 I am noticing slower performance with 15 disks (1 is a spare) in 
> RAID-6 (albeit slower 7200 ones, RE3s) than I was getting with 10 raptor150s 
> in RAID-6 (but I had used fdisk there).
>
> Justin.
>
>

Problem was barriers were enabled, that is why everything was slow but I 
would still like to know about the alignment.

Justin.

Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[Michal Soltys]

> 
> I am not worried about the filesystem as the defaults usually get it 
> right but with parted, this is the first time I had to use it for home 
> use and with RAID-6 I am noticing slower performance with 15 disks (1 is 
> a spare) in RAID-6 (albeit slower 7200 ones, RE3s) than I was getting 
> with 10 raptor150s in RAID-6 (but I had used fdisk there).
> 
> Justin.
> 

For best effect - partition should start at 1920th sector (stripe width
boundary), and su/sw should be appropriately set - su=64k,sw=13 in your
case. Parted shows the values normally - from the beginning of the 
volume, 0 based.


ps.

I dropped some of CCs.

Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[Justin Piszcz]

On Fri, 26 Dec 2008, Michal Soltys wrote:

>> 
>> I am not worried about the filesystem as the defaults usually get it right 
>> but with parted, this is the first time I had to use it for home use and 
>> with RAID-6 I am noticing slower performance with 15 disks (1 is a spare) 
>> in RAID-6 (albeit slower 7200 ones, RE3s) than I was getting with 10 
>> raptor150s in RAID-6 (but I had used fdisk there).
>> 
>> Justin.
>> 
>
> For best effect - partition should start at 1920th sector (stripe width
> boundary), and su/sw should be appropriately set - su=64k,sw=13 in your
> case. Parted shows the values normally - from the beginning of the volume, 0 
> based.
>
>
> ps.
>
> I dropped some of CCs.

Thanks.

Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[Josef 'Jeff' Sipek]

On Thu, Dec 25, 2008 at 06:46:37PM -0500, Justin Piszcz wrote:
> On Fri, 26 Dec 2008, Michal Soltys wrote:
> >> I am not worried about the filesystem as the defaults usually get it right 
> >> but with parted, this is the first time I had to use it for home use and 
> >> with RAID-6 I am noticing slower performance with 15 disks (1 is a spare) 
> >> in RAID-6 (albeit slower 7200 ones, RE3s) than I was getting with 10 
> >> raptor150s in RAID-6 (but I had used fdisk there).
> >> 
> >> Justin.
> >> 
> >
> > For best effect - partition should start at 1920th sector (stripe width
> > boundary), and su/sw should be appropriately set - su=64k,sw=13 in your
> > case. Parted shows the values normally - from the beginning of the volume, 0 
> > based.
> >
> >
> > ps.
> >
> > I dropped some of CCs.
> 
> Thanks.

It looks like you made why big partition. Why bother with partitioning at
all? If you just use the whole device, you _will_ be aligned properly if you
tell mkfs.xfs about the stripe unit/width.

Josef 'Jeff' Sipek.

-- 
All science is either physics or stamp collecting.
		- Ernest Rutherford

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Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[Justin Piszcz]

On Sat, 27 Dec 2008, Josef 'Jeff' Sipek wrote:

> On Thu, Dec 25, 2008 at 06:46:37PM -0500, Justin Piszcz wrote:
>> On Fri, 26 Dec 2008, Michal Soltys wrote:
>>>> I am not worried about the filesystem as the defaults usually get it right
>>>> but with parted, this is the first time I had to use it for home use and
>>>> with RAID-6 I am noticing slower performance with 15 disks (1 is a spare)
>>>> in RAID-6 (albeit slower 7200 ones, RE3s) than I was getting with 10
>>>> raptor150s in RAID-6 (but I had used fdisk there).
>>>>
>>>> Justin.
>>>>
>>>
>>> For best effect - partition should start at 1920th sector (stripe width
>>> boundary), and su/sw should be appropriately set - su=64k,sw=13 in your
>>> case. Parted shows the values normally - from the beginning of the volume, 0
>>> based.
>>>
>>>
>>> ps.
>>>
>>> I dropped some of CCs.
>>
>> Thanks.
>
> It looks like you made why big partition. Why bother with partitioning at
> all? If you just use the whole device, you _will_ be aligned properly if you
> tell mkfs.xfs about the stripe unit/width.
>
> Josef 'Jeff' Sipek.

Why bother partitioning?  I also run a Linux SW RAID1 on the host, as you 
know the drive letters can change when working on a server.

Example: Before I created the array (RAID-6), my disks were /dev/sda, 
/dev/sdb and /dev/sdc (spare), the RAID-6 was /dev/sdd.  After reboot, 
/dev/sdd became /dev/sda and /dev/sd[a-c] became /dev/sd[b-d].

In lilo.conf I had:
raid-extra-boot="/dev/sda,/dev/sdb"

If I ran LILO and forgot to fix the lilo.conf to reflect the new drive 
mappings:
raid-extra-boot="/dev/sdb,/dev/sdc"

I could be at risk of ruining the partition?

I try to avoid such situations when possible, to be safe.

Justin.

Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[Josef 'Jeff' Sipek]

On Sat, Dec 27, 2008 at 08:53:21AM -0500, Justin Piszcz wrote:
> Why bother partitioning?  I also run a Linux SW RAID1 on the host, as you 
> know the drive letters can change when working on a server.
>
> Example: Before I created the array (RAID-6), my disks were /dev/sda,  
> /dev/sdb and /dev/sdc (spare), the RAID-6 was /dev/sdd.  After reboot,  
> /dev/sdd became /dev/sda and /dev/sd[a-c] became /dev/sd[b-d].
>
> In lilo.conf I had:
> raid-extra-boot="/dev/sda,/dev/sdb"
>
> If I ran LILO and forgot to fix the lilo.conf to reflect the new drive  
> mappings:
> raid-extra-boot="/dev/sdb,/dev/sdc"
>
> I could be at risk of ruining the partition?

Hrm...interesting point. LILO could mess up the superblock in sector 0.

> I try to avoid such situations when possible, to be safe.

:)

I don't know how LILO would handle it, but I would try to use
/dev/disk/by-*/* instead of the rather unstable /dev/sd* names.

Just my 0.02 cents.

Jeff.

-- 
Keyboard not found!
Press F1 to enter Setup

Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[Justin Piszcz]

On Sat, 27 Dec 2008, Josef 'Jeff' Sipek wrote:

> On Sat, Dec 27, 2008 at 08:53:21AM -0500, Justin Piszcz wrote:
>> Why bother partitioning?  I also run a Linux SW RAID1 on the host, as you
>> know the drive letters can change when working on a server.
>>
>> Example: Before I created the array (RAID-6), my disks were /dev/sda,
>> /dev/sdb and /dev/sdc (spare), the RAID-6 was /dev/sdd.  After reboot,
>> /dev/sdd became /dev/sda and /dev/sd[a-c] became /dev/sd[b-d].
>>
>> In lilo.conf I had:
>> raid-extra-boot="/dev/sda,/dev/sdb"
>>
>> If I ran LILO and forgot to fix the lilo.conf to reflect the new drive
>> mappings:
>> raid-extra-boot="/dev/sdb,/dev/sdc"
>>
>> I could be at risk of ruining the partition?
>
> Hrm...interesting point. LILO could mess up the superblock in sector 0.
>
>> I try to avoid such situations when possible, to be safe.
>
> :)
>
> I don't know how LILO would handle it, but I would try to use
> /dev/disk/by-*/* instead of the rather unstable /dev/sd* names.
>
> Just my 0.02 cents.
>
> Jeff.

Excellent idea.

# lilo
Added 2.6.27.9-1
Added 2.6.27.10-1
Added 2.6.27.10-2 *
The boot record of  /dev/md1  has been updated.
The boot record of  /dev/disk/by-id/scsi-SATA_WDC_WD1500ADFS-_WD-SN#######  has been updated.
Warning: /dev/disk/by-id/scsi-SATA_WDC_WD1500ADFD-_WD-SN######## is not on the first disk
The boot record of  /dev/disk/by-id/scsi-SATA_WDC_WD1500ADFD-_WD-SN########  has been updated.

Thanks!

Justin.

Re: How do I tell if my partition is aligned for a 64k/RAID-6?

[John Robinson]

On 27/12/2008 13:58, Josef 'Jeff' Sipek wrote:
> 
> --
> Keyboard not found! Press F1 to enter Setup

I thought the original was
   Keyboard not found! Press any key to continue

Cheers,

John.