This post is more than 5 years old
265 Posts
1
2557
TDAT Device sizes for maximum performance
Hi all
from the document Simplified VMAX Blueprint Guide
VMAX + 5874 & 75 EMC Enginuity™
Solutions Enabler v7 which is in EMC speed
it said to create TDAT devices with 259912 cyl = 236.49 GB on 1000GB SATA drive with Raid6(6+2)
while other document direct us to have at least 8 hypers per disk
if i create 236.49 TDAT on 1000 GB R6(6+2) i will end up with < 4 hypers perdisk
so what the best practics on that, the same goes for other disk sizes and disk groups, the documents contradict each other.
I am looking for the best perofrmance for an environment based completley on Thin provisoning and FAST VP.
I got this from the document mentioned:
for 1TB drives please use the following TDAT device size:
RAID6 (6+2)
device size = 259912 CYL = 237.96 GB
total devices per group 23
---------------------------------
for 450GB Drives
RAID 6 (6+2)
Device size= 260570 CYL =238.56 GB
total devices per group 10
-------------------
for 450GB Drives
RAID 1 (2 drives)
Device size= 54282 CYL= 49.70 GB
total devices per group 8
------------------
For 300 GB
RAID 1 (2 drives)
Device size =35960 CYL = 32.92 GB
Total devices per group 8
----------------------
Quincy561
1.3K Posts
0
May 25th, 2011 07:00
Yes you are missing something.
One volume on 236GB 6+2 volume will create 8 physical hypers on 8 drives. Each drive will have a ~39.3GB split or hyper on it (39.3 x 6 = 235.8 usable capacity) The two parity overheads don't count for the usable capacity, but take up space on the 8 drives.
Quincy561
1.3K Posts
0
May 25th, 2011 06:00
Yes, you want a minimum of 8 physical hypers per drive.
With a 1TB drive in 6+2 the minimum number of hypers you can have and use all the capacity is 26 hypers using the largest volume size allowed.
Quincy561
1.3K Posts
0
May 25th, 2011 06:00
Your comment "if i create 236.49 TDAT on 1000 GB R6(6+2) i will end up with < 4 hypers perdisk" is incorrect. You will have 6,000GB usable across the 8 drives. Divide that by 236.49 = 25.37 hypers. I would make the volumes slightly smaller to end up with an even number.
Quincy561
1.3K Posts
1
May 25th, 2011 07:00
Maybe a picture will help. This is a RAID5 7+1 layout with 9GB volumes on 73GB drives. 56 physical hypers per disk.
1 Attachment
Hyper Layout.ppt
Mosa3lyan
265 Posts
0
May 25th, 2011 07:00
hi Quincy56
6000/236=25 hypers on the whole raid group ( 6+2)
so its 25/8= 3 hypers per disk <4
and 236 is based on the document
Am i right or missing something ???
Mosa3lyan
265 Posts
0
May 25th, 2011 07:00
THANKKKKKKKKKKKKKKK
YOUUUUUUUUUUUUUUUUUUUUUUUUU
VERYYYYYYYYYYYYYYYY
MUCHHHHHHHHHHHHHHH
Quincy561
1.3K Posts
0
May 25th, 2011 08:00
If you are using RAID6, there is zero risk from losing data with 2 drives failing. You have to lose 3 in a raid group.
With RAID5, there is some risk, however low. If you have RDF/S that risk is removed. So it depends on the tolerance for risk, and the other protection methods you have.
You need enough drives in the pool to support the workload that is going to be put on them.
Mosa3lyan
265 Posts
0
May 25th, 2011 08:00
is there any recommended number for number of physicall disk allocated to virtual pool
or number of tdat in a pool
Mosa3lyan
265 Posts
0
May 25th, 2011 08:00
Hi Quincy56
i have another 2 question regarding Virtual Pool
What is the recommended number of TDAT to put in a Thin pool,if i put too many TDAT devices in a thin pool as it increases the risk of data loss in case of double disk failure!! Is there a recommended number?
and for Virtual pool . I am building Virtual Pool on Disk Group A that have 150 disk and consuming all the size on DG(A) for creating TDAT to my Virtual pool
is it ok to have 150 disk for virtual pool or should i create more disk group and more virtual pool , what the recommended number of disk allocated to virtual pool taking in consideration performance and HA
Quincy561
1.3K Posts
1
May 25th, 2011 08:00
As many as you need for performance, capacity and isolation if desired.
The easiest is to have all drives of one technology and protection in one pool, but that may not be practical for some of the above considerations.
I think the VP paper on Powerlink discusses this.