Please explaine the symdisk command. 2

[vptl]

Hi,
I see following with my symdisk command. I have few questions with it. Appriciate the help.

Director : DF-1A
Interface : C
Target ID : 0
Disk Group Number : 1

Vendor ID : SEAGATE
Product ID : SX3146807FC
Product Revision : CH146LF
Serial ID : 3HY0RV8R

Disk Blocks : 286339876
Block Size : 512
Actual Disk Blocks : 286749475
Total Disk Capacity (MB) : 139814
Free Disk Capacity (MB) : 1701
Actual Disk Capacity (MB) : 140014
Hot Spare : False


Hypers (17):
{
# Vol Emulation Dev Type Mirror Status Cap(MB)
-- --- ---------------- ---- ------------- ------ -------------- --------
1 1 FBA 0004 Data 1 Ready 8
2 2 FBA 0027 RAID-S Data 1 Ready 8632
8 8 FBA 00A7 RAID-S Data 1 Ready 8632
5 5 FBA 00C7 RAID-S Data 1 Ready 8632
3 3 FBA 0144 RAID-S Parity 2 Ready 8632
6 6 FBA 0187 RAID-S Data 1 Ready 8632
4 4 FBA 01A7 RAID-S Data 1 Ready 8632
9 9 FBA 01C7 RAID-S Data 1 Ready 8632
7 7 FBA 0250 RAID-S Parity 2 Ready 8632
10 10 FBA 0253 RAID-S Data 1 Ready 8632
13 13 FBA 0293 RAID-S Parity 2 Ready 8632
11 11 FBA 02DF RAID-S Data 1 Ready 8632
14 14 FBA 02FF RAID-S Data 1 Ready 8632
12 12 FBA 033F RAID-S Data 1 Ready 8632
15 15 FBA 03AB RAID-S Data 1 Ready 8632
16 16 FBA 040B RAID-S Data 1 Ready 8632
17 17 FBA 041F RAID-S Parity 2 Ready 8632
}

Questions.
1. What is the clmn Vol refers to ?
2. If I create RAID-S type symdev why my symdev is mentioned as either data or parity only ? arn't they suppose to be spread across few physical spindles with 3 chunk of data and one chunk of parity ?
3. clmn 7 once it is RAID-s what are the mirror #s there ?

This came up when I was trying to find out how my physical spindles are allocated.

Thanks in advance.
VPTL.

 

[culainn]

Hi VPTL,
hope this answers some of your questions.
1.vol# - not sure of, would have said it is the hyper number of the logical on disk but its already got a column for that. It may be the raid rank.
2. Not sure what you mean here, if you mean why are there multiple paritys on the same disk, its because you will have multiple raid ranks going across the disk.
3. the mirror column if you notice shows all the data devs as M1 and parity as M2. This is just an EMC way of telling you that the protection for the data is the parity. Doesn't read very well but there you go,
all the best,
Colin

 

[vptl]

A1.
As always expected from you...very valuable info.

A2. Let me come again for this one.
See the questions bellow.

Symdev -noport list | grep 578

0578 Not Visible ???:? 15A7 RAID-S N/Grp'd RW 8632

From symdisk

Director : DF-15A
Interface : D
Target ID : 7
Disk Group Number : 2

Vendor ID : IBM
Product ID : IX35L146EFDY10-0
Product Revision : IBM146F
Serial ID : ECVN0GAC

Disk Blocks : 286339876
Block Size : 512
Actual Disk Blocks : 286749475
Total Disk Capacity (MB) : 139814
Free Disk Capacity (MB) : 113919
Actual Disk Capacity (MB) : 140014
Hot Spare : False





From show dev

Device Physical Name : Not Visible

Device Symmetrix Name : 0578
Device Serial ID : N/A
Symmetrix ID : 000187700687

Attached BCV Device : N/A

Attached VDEV TGT Device : N/A

Vendor ID : EMC
Product ID : SYMMETRIX
Product Revision : 5670

Device Emulation Type : FBA
Device Defined Label Type: N/A
Device Defined Label : N/A
Device Sub System Id : 0x0002

Device Block Size : 512

Device Capacity
{
Cylinders : 18414
Tracks : 276210
512-byte Blocks : 17677440
MegaBytes : 8632
KiloBytes : 8838720
}

Device Configuration : RAID-S (3+1) (Non-Exclusive Access)

Device is WORM Enabled : No
Device is WORM Protected : No

SCSI-3 Persistent Reserve: Disabled

Dynamic Spare Invoked : No

Dynamic RDF Capability : None

Device Service State : Normal

Device Status : Ready (RW)
Device SA Status : N/A (N/A)

Mirror Set Type : [RAID-S Data,RAID-S Parity,N/A,N/A]

Mirror Set DA Status : [RW,RW,N/A,N/A]

Mirror Set Inv. Tracks : [0,0,0,0]

Back End Disk Director Information
{
Hyper Type : RAID-S Data
Hyper Status : Ready (RW)
Disk [Director, Interface, TID] : [01B, C, 7]
RAID-S group Number : 8175
Disk Director Volume Number : 51
Hyper Number : 1
Disk Capacity : 139814m
Disk Group Number : 2

Hyper Type : RAID-S Parity
Hyper Status : Ready (RW)
Disk [Director, Interface, TID] : [15A, D, 7]
RAID-S group Number : 8175
Disk Director Volume Number : 115
Hyper Number : 1
Disk Capacity : 139814m
Disk Group Number : 2
}

Now the question is I carve dev 578 in RAID-S config. So If I understand correctlly this device is cut from 4 physical disks 3 of which will hase data and one will be parity.
If so then
1. why symdisk is showing 578 as RAID-S Parity ?
2. What is the meaning of "Back End Disk Director Information" section in show dev which indicates that this dev is connected to 01B AS RAID-S DATA And at the same time at 15A as RAID-S PARITY ?
3. What is the meaning (Assosiation) of three devices showed in symdisk out put ?

A3.
Got it. Thanks.


Really appriciate your very valuable help.


Thanks.
V.

 

[culainn]

okay I think I got you this time. There may be a bit of confusion between Raid-s and Raid-5.
If you think of a physical disk like the one in the symdisk disk command, there are a number of devices or hypers on the disk, (we call for eaxmple this disk 1). EMC in Raid-s will take a hyper from disk 1 a hyper from disk 2 and a hyper from disk 3. It will Xor the dat from these three hypers together to come up with the parity.
Emc in Raid-s for an individual hyper does not stripe across 3 disks i.e. if you have a 9gb hyper the hyper will exist on one physical disk, it will not be 3x3gb hypers on 3 seperate disks.
Raid-5 works more like you described.
hope I got it right this time.
Colin

 

[vptl]

Ok, under stood but then why (I missed in previous post.)
I see sym dev 578 as RAID-S PARITY IN SYMDISK, Since I am going to write data on it (As it iscarved for data, NO ? )
the Parity portion of my data should not be on sym dev 578 ?

Director : DF-15A
Interface : D
Target ID : 7
Disk Group Number : 2

Vendor ID : IBM
Product ID : IX35L146EFDY10-0
Product Revision : IBM146F
Serial ID : ECVN0GAC

Disk Blocks : 286339876
Block Size : 512
Actual Disk Blocks : 286749475
Total Disk Capacity (MB) : 139814
Free Disk Capacity (MB) : 113919
Actual Disk Capacity (MB) : 140014
Hot Spare : False


Hypers (3):
{
# Vol Emulation Dev Type Mirror Status Cap(MB)
-- --- ---------------- ---- ------------- ------ -------------- --------
3 117 FBA 04D8 RAID-S Data 1 Ready 8632
2 116 FBA 0538 RAID-S Data 1 Ready 8632
1 115 FBA 0578 RAID-S Parity 2 Ready 8632
}

As you can see here...

Thanks.

 

[Gotraidbox]

Raid-S uses four different physical disk drives: 3 are data and the fourth is parity. Any one can be hot-swapped out and the data will be reconstructed and rewritten from the remaining three.

 

[vptl]

That is ok, but why sym dev 578 is labeled as RAID-S Parity and 538 & 4D8 are as RAID-S DATA ?
Arn't they all suppose to be RAID-S DATA ?

Thakns.

 

[culainn]

hmmmm....good point, this might be an EMC-ism. OK lets think about this. We can write to the xD device but we cannot write to the xP device. The xD is an addressable unit of storage the xP is not. I wonder if you issued the same symdev command on 4D8 and 538 would you get 4D8 showing up as xP. Can you try and post the result.
Cheers,

 

[vptl]

The information is a portion of a "symdisk -sid xxx -v -hypers list " command. I searched for 578 from the output file and this is where it was.

I also confirmed that 4D8 is a symdev and is allocated to SAN cleint. 538 is still in noport pool. !

Thanks.

 

[vptl]

I think I got it now..
The symdev is not just a refrance to a single hyper but also to it's M2 device. In RAID-1 it will be mirror disk hyper but in RAID-S it will be parity volume. (As from your previous post about M1 & M2 device in RAID-S)

SO when we do symdisk command, symdev shows up two places..1 for it's data volume ( data Hyper) and 1 for it's m2 devices (or parity vol (parity Hyper) )!.
That is why all RAID-S symdev will have atleast one instance stating RAID-S Parity in symdisk command.
I also confirmed this with RAID-1 type symdev.
Please correct me if I am wrong.
Thanks for your great help...with out that I would never reach to this conclusion.

Thanks,
Vimal.

 

[vptl]

In this case...another question arise is why the size of parity volume is also same as Data volume (Hyper) ?

 

[culainn]

the reason it needs to be the same size is because for each track on the 3 data disks we are Xor'ing together so we get one parity track that is written to the parity disk.
as regards the other thing...good job I think you have it cracked...

 

[vptl]

Got you...so the 578 RAID-S PARITY Hyper do not just belongs to 578 RAID-S DATA hyper but it will also host (on the same physical track) PARITY FOR TWO more RAID-S DATA DEVS ?
I know it gets complex here...but I this that shoul be the case...Please confirm.
This was very important for me as I am writing a script to map sym dev and spindles instead of going to EMC for bin file...(Which EMC do not prefer at this site.!!)

 

[culainn]

Hi, I think what you are saying is correct, but I would double check with EMC.
Colin

 

[Chacalinc]

vptl, remember that a RAID-S config stand for 4 disk drives, where 3 are data and 1 parity, so if you see that the device 578 is a parity volume, then it belong to the 578 data volume plus 2 more devices.

example:

D1 D2 D3 D4
00 01 02 02P
03 04 04P 05
06 06P 07 08

D1, D2, D3 and D4 stand for Disk 1, 2 3 and 4. 02P is the parity volume for devices 00, 01 and 02. In your case, 578P is the parity volume for 578 (data) and 2 more devices.

Hope this helps.

 

[vptl]

Thanks. It is very complex to understand...But I think now I have some idea abt this...and that should be enough..
Thanks a lot.