Striped Logical Volume and RAID 5

Striped Logical Volume and RAID 5

Post by amshai.. » Fri, 26 Jan 2001 06:33:28



Hi there,

We are using RAID 5 on our ESS, will making a stripe logical volume
along with mirroring on it will improve any performance or what, I
believe RAID 5 is already striped or spread across disks and creating a
striped logical volume will create additional overheads, which will not
give any boast to performance.

Arshad

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Striped Logical Volume and RAID 5

Post by jthom.. » Fri, 26 Jan 2001 07:09:05


We have had the same discussion at our shop:  you are creating
a "plaid" of intersecting stipes.

I think the idea behind raid 5 is that it gives the most redundancy
with the FEWEST disks, so it's cheaper than mirroring large numbers of
disks.

If you are running oracle, or something like it that wants the I/O
spread out over a lot of spindles, then simple mirroring is probably
the way to go instead.

 But you can stripe across multiple raid 5 volumes.... but I think
stripe width would determine whether the I/O is actually distributed
evenly or not.



> Hi there,

> We are using RAID 5 on our ESS, will making a stripe logical volume
> along with mirroring on it will improve any performance or what, I
> believe RAID 5 is already striped or spread across disks and creating
a
> striped logical volume will create additional overheads, which will
not
> give any boast to performance.

> Arshad

> Sent via Deja.com
> http://www.deja.com/

Sent via Deja.com
http://www.deja.com/

 
 
 

Striped Logical Volume and RAID 5

Post by Urban A. Haa » Fri, 26 Jan 2001 07:37:17


The ESS does stripe the data within it's LSS RAID rank. You can get
performance benefits my striping the data among hdisks / vpaths created on
different LSSs, depending on how much disk is in the ESS. (Meaning assign a
chunk from each RAID-5 piece on the ESS to your system, then make a volume
group out of those hdisks or vpaths if using SDD/DPO and make a striped lv
on each of those hdisks.) You really want to take this approach of making
your vgs out of small pieces out of each LSS and saving space in each LSS in
case you want to setup FlashCopies later.

I wouldn't mirror the data, because you defeat some of the performance
gaining techniques in the cache on the ESS, but this is theoretical and I
haven't benchmarked it yet.

BTW, I haven't created striped LVs on the ESS, mostly because I was getting
such great throughput out of the shark, I haven't needed it.

--
Urban A. Haas
CEO - Urban Technology, Inc.
Minneapolis, MN  USA
Phone: (952) 595-8810    Fax: (952) 595-8710

Web: http://www.urbantechnology.com

This e-mail was composed of 100% recycled bits.


> Hi there,

> We are using RAID 5 on our ESS, will making a stripe logical volume
> along with mirroring on it will improve any performance or what, I
> believe RAID 5 is already striped or spread across disks and creating a
> striped logical volume will create additional overheads, which will not
> give any boast to performance.

> Arshad

> Sent via Deja.com
> http://www.deja.com/

 
 
 

Striped Logical Volume and RAID 5

Post by Urban A. Haa » Fri, 26 Jan 2001 07:40:59


The ESS actually has five steps of Cache algorithm to reduce writes to
actual disk that actually makes RAID-5 implementation underneath faster than
mirroring in a JBOD configuration. There are algorithms the IBM has
developed unique to the Shark that accomplish this.

While your statement about mirroring is generally true, in the case of the
shark, it should not be the case. There's one presentation I've seen on this
where there are five steps to reduce I/O. I've tested throughput on this box
and it was incredible.

--
Urban A. Haas
CEO - Urban Technology, Inc.
Minneapolis, MN  USA
Phone: (952) 595-8810    Fax: (952) 595-8710

Web: http://www.urbantechnology.com

This e-mail was composed of 100% recycled bits.


> We have had the same discussion at our shop:  you are creating
> a "plaid" of intersecting stipes.

> I think the idea behind raid 5 is that it gives the most redundancy
> with the FEWEST disks, so it's cheaper than mirroring large numbers of
> disks.

> If you are running oracle, or something like it that wants the I/O
> spread out over a lot of spindles, then simple mirroring is probably
> the way to go instead.

>  But you can stripe across multiple raid 5 volumes.... but I think
> stripe width would determine whether the I/O is actually distributed
> evenly or not.



> > Hi there,

> > We are using RAID 5 on our ESS, will making a stripe logical volume
> > along with mirroring on it will improve any performance or what, I
> > believe RAID 5 is already striped or spread across disks and creating
> a
> > striped logical volume will create additional overheads, which will
> not
> > give any boast to performance.

> > Arshad

> > Sent via Deja.com
> > http://www.deja.com/

> Sent via Deja.com
> http://www.deja.com/