How is th RIAD-S works ? (Dedicated Parity ? /Shared ? )

[vptl]

RAID-S in DMX frames is it a Dedicated parity patter or shared ?

Also what is the diffrance between

Veritas Raid 5 Vs DMX RAID-S

DMX RAID-S Vs DMX Parity Raid.

Thanks

 

[Chacalinc]

RAID S is like RAID 5, but it has a big difference:

RAID 5 spread the parity between all disk drives and parity is for chunks of data (blocks with a fixed size), so a chunk size could be 128K, 32K, etc. depending on the provider.

D D D D P
D D D P D
D D P D D
D P D D D
P D D D D

Each column is a disk drive. D stand for "Data" and P for "Parity".

RAID S is done with 4 disk (not more, not less) and it use a hypervolume (as partitions) rather than blocks, so you have data volumes and parity volumes. For example, if you have 4 disk drives in RAID S, and each drive with 4 hypervolume you will have:

V V V P
V V P V
V P V V
P V V V

Each column is a disk drive. V stand for "Data VOLUME" and P for "Parity VOLUME". A volume is a LUN assigned to servers.
The Parity volume on first row is the parity for the 3 Volumes on first row; second parity volume (2nd row) is for 3 volumes on 2nd row, and so on...

Do you get the big difference?

Veritas RAID 5 is, as the name state, a RAID 5 and the difference is the stated above, it means striped data and striped parity.

Hope this help.

 

[comtec17]

Let it be known that RAID-S is a poor performer as well. As an example, I did a test restoring a 1TB SQL server to an EMC Symmetrix 8000 using RAID-S and it took 32 hours to create the SQL volume space before the restore even started. I performed the same exact test using a HDS 7700e (old technology) in RAID-5 and I was able to build the 1TB SQL volume in 3.5 hours. That saved me 28.5 hours of recovery time. Of course we went with a RAID-5 array.

 

[Chacalinc]

That's true comtect17, 8000 series don't have a good performance in RAID-S... I guess you use 36 GB disk drives for your test, correct? with 73 GB drives is not even permited! (very very poor performance). With 8000 series, the best config is RAID 1 (1/0).

With DMX series is not the same, DMX series use FC disk drives and the architecture is quite different, and best processors in directors.

 

[vptl]

Thanks a lot Chacalinc. This is great explnation I ever had for RAID-S. Great job. Really appriciate.

After reading comtec17's note...one more thing..

What do you think will be best choise if I have option to use locally attached FC DISK ARRAY ( Where I can use RAID-5) as compare to useing DMX wilth RAID-S.

Do you or comtec has any practical expeiments on this as one of my client is demanding for best performance setup.

Also can you please explain what is the gatekeeprs in symmetrix and why do we need atleast 5 of them in DMX ?

Thanks,
Vimal.

 

[Chacalinc]

Vimal,

Regarding to gatekeepers, you posted a question on thread511-756438 titled "what is the gatekeeper in symmetrix frame ?" ( thread511-756438 ) where two of us explain it to you.

Do you need more info besides that response? if so, just let us know )

If you want the best performance, RAID 1/o is the best, but if you need the best performance, with less cost (that RAID 1) use DMX with RAID-S. (avoid to use big disk drives, I mean 146 GB drives). DMX has an excellent archutecture, full fibre, an excellent cache algoritm, so if you going to put an OLTP data bases, this is the best option.

Cheers.

 

[vptl]

Yes I am still confused abut the role of the gatekeeper and hence the minimum no. of gatekeeper requrement.


Thanks,
Vimal.

 

[Chacalinc]

to respond your question, could you tell us what EMC software are you running with the Symemtrix boxes?

 

[culainn]

Hi,
me again, the amount of gatekeepers you require depends on what EMC software you have purchased and the different flavours of the software. What I normally do is for each bit of software have two gatekeepers. EMC will tell what software requires gatekeepers and what does not. i.e. powerpath does not need gatekeepers, timefinder does etc.. Another important point to note is that it is bad to have gatekeepers under multipathing software, a good recomendation is to have 2 gatekeepers but assign one down one path and the other down the other path thereby you won't run into any locking issues.
Cheers,
Colin.

 

[vptl]

Thanks Culainn,
But what is the reason or what do they do in the process of passing the i/o from the FA to the disk/EMC cache mechanism.

Can I compare these device with private reigons in Veritas ?

Thanks again.
Vptl.