Raid 10 or Raid 5?

Is raid 10 better than 5 with only 3 h/drives. Does no of h/drives matter ?Yes it does matter.
Raid 10 is faster than Raid 5, however it will need twice
the number of disks. So if you have two disjs of 10 gb
each, the most you can get out of them is 10 gb NOT 20.
Raid 5 is slower but is better with disks so you will get
more space.
As you only have a couple of disks I sugest raid 5
J
>--Original Message--
>Is raid 10 better than 5 with only 3 h/drives. Does no of
h/drives matter ?
>.
>|||depends on your needs. If READ is the primary function, RAID5 makes
sense because its less costly, but write is primary function
RAID10(0+1) is the best solution.|||But she can't do a RAID 10 with just 3 drives. It's either a Raid 1 and you
loose a drive or Raid 5.
--
Andrew J. Kelly
SQL Server MVP
<sightdev@.yahoo.com> wrote in message
news:9861f5eb.0401300736.6761b95d@.posting.google.com...
> depends on your needs. If READ is the primary function, RAID5 makes
> sense because its less costly, but write is primary function
> RAID10(0+1) is the best solution.|||A word of warning. I discovered my expensive Dell Perc3/DC controllers
implement Raid 10 as a span (concatenation) of mirrors not a stripe.
I have 22 disks and over half are idle.
I'm having to split the database file and log file into pieces.
Paul
"Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
news:ucSRJy05DHA.2560@.TK2MSFTNGP09.phx.gbl...
> But she can't do a RAID 10 with just 3 drives. It's either a Raid 1 and
you
> loose a drive or Raid 5.
> --
> Andrew J. Kelly
> SQL Server MVP
>
> <sightdev@.yahoo.com> wrote in message
> news:9861f5eb.0401300736.6761b95d@.posting.google.com...
> > depends on your needs. If READ is the primary function, RAID5 makes
> > sense because its less costly, but write is primary function
> > RAID10(0+1) is the best solution.
>|||Paul,
Not sure what you mean exactly. The RAID numbers often get confusing when
it comes to 1+0 or 0+1. One will be a stripe of mirrors and the other is a
mirror of stripes. The difference is mainly in the redundancy as the stripe
of mirrors will tolerate potentially more failures than a mirror of stripes.
In either case all the disks are used but you only get half the usable disk
space. That is how Raid arrays work. You sacrifice drives for redundancy
and speed. I don't know why you say you need to split your files. That
should not be necessary.
--
Andrew J. Kelly
SQL Server MVP
"Paul Cahill" <XYZpaul.cahillXYZ@.blueyonder.co.uk> wrote in message
news:eyHa3nY6DHA.2264@.tk2msftngp13.phx.gbl...
> A word of warning. I discovered my expensive Dell Perc3/DC controllers
> implement Raid 10 as a span (concatenation) of mirrors not a stripe.
> I have 22 disks and over half are idle.
> I'm having to split the database file and log file into pieces.
> Paul
>
> "Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
> news:ucSRJy05DHA.2560@.TK2MSFTNGP09.phx.gbl...
> > But she can't do a RAID 10 with just 3 drives. It's either a Raid 1 and
> you
> > loose a drive or Raid 5.
> >
> > --
> >
> > Andrew J. Kelly
> > SQL Server MVP
> >
> >
> > <sightdev@.yahoo.com> wrote in message
> > news:9861f5eb.0401300736.6761b95d@.posting.google.com...
> > > depends on your needs. If READ is the primary function, RAID5 makes
> > > sense because its less costly, but write is primary function
> > > RAID10(0+1) is the best solution.
> >
> >
>|||You are correct on the raid levels and raid 10 is defined as a stripe of
mirrors. However Dell's documentation for the Perc3 and other controllers
now states (and it's true) that their implementation of raid 10 is a span of
mirrors. ie if you have a raid 10 of four 18GB disks and you create a 9GB
log file the file will wholy reside on the first mirror pair. The second
mirror pair will not be used until the 1st mirror pair is full.
This explains the dissappointing performance we have from our 22 disk
system. Although I benchmarked it, the one thing I did not do when I set it
up was to watch the disk lights.
For example our log file does indeed live on a 4 disk raid 10 array of 18GB
15K drives. The log file is smaller than 18GB. When I/O occurs only two of
the disk lights flash. The other two never flash. If it was true raid 10
then all 4 lights should flash as the i/o is striped.
So I'm having to do the striping myself by spitting the files across raid
arrays. ie Indexes on one, certain tables on another. Not a bad thing
anyway I guess. But if I'd known about dell's Raid 10 I'd have planned
differently. It's not east to make changes on a 24/7 system.
An alternative with the dell perc3 would be to stripe the drives (Raid 0)
and then mirror using the O/S. Not one I care to choose.
Paul
http://docs.us.dell.com/docs/storage/perc3dc/ug/en/Levels.htm
The above document describes Raid 10 on the perc3/dc as a stripe of mirrors
http://docs.us.dell.com/docs/software/smarrman/marb32/ch8_perc.htm
This document shows that perc3/dc implements as a concatenation
Search for string "Supported RAID Levels for PERC Subsystem Controllers"
http://docs.us.dell.com/docs/software/smarrman/marb32/ch3_stor.htm#1037893
This document describes spanned disks
"Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
news:uXdx2uZ6DHA.2952@.TK2MSFTNGP09.phx.gbl...
> Paul,
> Not sure what you mean exactly. The RAID numbers often get confusing when
> it comes to 1+0 or 0+1. One will be a stripe of mirrors and the other is
a
> mirror of stripes. The difference is mainly in the redundancy as the
stripe
> of mirrors will tolerate potentially more failures than a mirror of
stripes.
> In either case all the disks are used but you only get half the usable
disk
> space. That is how Raid arrays work. You sacrifice drives for redundancy
> and speed. I don't know why you say you need to split your files. That
> should not be necessary.
> --
> Andrew J. Kelly
> SQL Server MVP
>
> "Paul Cahill" <XYZpaul.cahillXYZ@.blueyonder.co.uk> wrote in message
> news:eyHa3nY6DHA.2264@.tk2msftngp13.phx.gbl...
> > A word of warning. I discovered my expensive Dell Perc3/DC controllers
> > implement Raid 10 as a span (concatenation) of mirrors not a stripe.
> > I have 22 disks and over half are idle.
> > I'm having to split the database file and log file into pieces.
> >
> > Paul
> >
> >
> > "Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
> > news:ucSRJy05DHA.2560@.TK2MSFTNGP09.phx.gbl...
> > > But she can't do a RAID 10 with just 3 drives. It's either a Raid 1
and
> > you
> > > loose a drive or Raid 5.
> > >
> > > --
> > >
> > > Andrew J. Kelly
> > > SQL Server MVP
> > >
> > >
> > > <sightdev@.yahoo.com> wrote in message
> > > news:9861f5eb.0401300736.6761b95d@.posting.google.com...
> > > > depends on your needs. If READ is the primary function, RAID5 makes
> > > > sense because its less costly, but write is primary function
> > > > RAID10(0+1) is the best solution.
> > >
> > >
> >
> >
>|||Paul,
I have to admit I don't know exactly what they are referring to. Hopefully
I can read more on it later but it doesn't sound pretty. I would call and
talk to someone in tech support directly who says claims they know what they
are talking about when it comes to this implementation of RAID 10 to get his
take. If it's anything close to what the docs state I would ask for my
money back since that is no where close to the definition of RAID 10 that I
have ever seen and I don't know how they can even claim it as such. From
what I gather the reason why the other disks lights are not blinking is that
with "concatenation" it fills up the first disk before it moves to the next
and you probably don't have enough data on it yet. Hopefully we are just
misreading their information but in either case I wish you luck.
Andrew J. Kelly
SQL Server MVP
"Paul Cahill" <XYZpaul.cahillXYZ@.blueyonder.co.uk> wrote in message
news:OYmMKUj6DHA.1936@.TK2MSFTNGP12.phx.gbl...
> You are correct on the raid levels and raid 10 is defined as a stripe of
> mirrors. However Dell's documentation for the Perc3 and other controllers
> now states (and it's true) that their implementation of raid 10 is a span
of
> mirrors. ie if you have a raid 10 of four 18GB disks and you create a 9GB
> log file the file will wholy reside on the first mirror pair. The second
> mirror pair will not be used until the 1st mirror pair is full.
> This explains the dissappointing performance we have from our 22 disk
> system. Although I benchmarked it, the one thing I did not do when I set
it
> up was to watch the disk lights.
> For example our log file does indeed live on a 4 disk raid 10 array of
18GB
> 15K drives. The log file is smaller than 18GB. When I/O occurs only two of
> the disk lights flash. The other two never flash. If it was true raid 10
> then all 4 lights should flash as the i/o is striped.
> So I'm having to do the striping myself by spitting the files across raid
> arrays. ie Indexes on one, certain tables on another. Not a bad thing
> anyway I guess. But if I'd known about dell's Raid 10 I'd have planned
> differently. It's not east to make changes on a 24/7 system.
> An alternative with the dell perc3 would be to stripe the drives (Raid 0)
> and then mirror using the O/S. Not one I care to choose.
> Paul
> http://docs.us.dell.com/docs/storage/perc3dc/ug/en/Levels.htm
> The above document describes Raid 10 on the perc3/dc as a stripe of
mirrors
>
> http://docs.us.dell.com/docs/software/smarrman/marb32/ch8_perc.htm
> This document shows that perc3/dc implements as a concatenation
> Search for string "Supported RAID Levels for PERC Subsystem Controllers"
>
> http://docs.us.dell.com/docs/software/smarrman/marb32/ch3_stor.htm#1037893
> This document describes spanned disks
>
> "Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
> news:uXdx2uZ6DHA.2952@.TK2MSFTNGP09.phx.gbl...
> > Paul,
> >
> > Not sure what you mean exactly. The RAID numbers often get confusing
when
> > it comes to 1+0 or 0+1. One will be a stripe of mirrors and the other
is
> a
> > mirror of stripes. The difference is mainly in the redundancy as the
> stripe
> > of mirrors will tolerate potentially more failures than a mirror of
> stripes.
> > In either case all the disks are used but you only get half the usable
> disk
> > space. That is how Raid arrays work. You sacrifice drives for
redundancy
> > and speed. I don't know why you say you need to split your files. That
> > should not be necessary.
> >
> > --
> >
> > Andrew J. Kelly
> > SQL Server MVP
> >
> >
> > "Paul Cahill" <XYZpaul.cahillXYZ@.blueyonder.co.uk> wrote in message
> > news:eyHa3nY6DHA.2264@.tk2msftngp13.phx.gbl...
> > > A word of warning. I discovered my expensive Dell Perc3/DC controllers
> > > implement Raid 10 as a span (concatenation) of mirrors not a stripe.
> > > I have 22 disks and over half are idle.
> > > I'm having to split the database file and log file into pieces.
> > >
> > > Paul
> > >
> > >
> > > "Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
> > > news:ucSRJy05DHA.2560@.TK2MSFTNGP09.phx.gbl...
> > > > But she can't do a RAID 10 with just 3 drives. It's either a Raid 1
> and
> > > you
> > > > loose a drive or Raid 5.
> > > >
> > > > --
> > > >
> > > > Andrew J. Kelly
> > > > SQL Server MVP
> > > >
> > > >
> > > > <sightdev@.yahoo.com> wrote in message
> > > > news:9861f5eb.0401300736.6761b95d@.posting.google.com...
> > > > > depends on your needs. If READ is the primary function, RAID5
makes
> > > > > sense because its less costly, but write is primary function
> > > > > RAID10(0+1) is the best solution.
> > > >
> > > >
> > >
> > >
> >
> >
>|||I am taking this up with Dell, others are discussing this in the Dell Talk
forum.
The sales guys and the 1st line tech support people don't even understand
the issue.
At the moment I'm getting unfufilled call back promises.
My main data file is on a (Dell) raid 10 of 6 disks 18GB disks. The main
data file is over 36GB. If I watch the lights on this logical array they do
all flash but not together. You can see it happening in pairs. If I/O on the
data file was truly random then I would be getting some bangs for all my
bucks but of course there are always hotspots in data access.
No single i/o will ever proceed faster than the speed of a single 18GB 15K
drive.
The only way I can see around this is to stripe using the perc3 and then
mirror the stripe using the operating system. Not a route I am prepared to
proceed with.
Paul
"Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
news:eImaq%23l6DHA.2480@.TK2MSFTNGP10.phx.gbl...
> Paul,
> I have to admit I don't know exactly what they are referring to.
Hopefully
> I can read more on it later but it doesn't sound pretty. I would call and
> talk to someone in tech support directly who says claims they know what
they
> are talking about when it comes to this implementation of RAID 10 to get
his
> take. If it's anything close to what the docs state I would ask for my
> money back since that is no where close to the definition of RAID 10 that
I
> have ever seen and I don't know how they can even claim it as such. From
> what I gather the reason why the other disks lights are not blinking is
that
> with "concatenation" it fills up the first disk before it moves to the
next
> and you probably don't have enough data on it yet. Hopefully we are just
> misreading their information but in either case I wish you luck.
>
>
> --
> Andrew J. Kelly
> SQL Server MVP
>
> "Paul Cahill" <XYZpaul.cahillXYZ@.blueyonder.co.uk> wrote in message
> news:OYmMKUj6DHA.1936@.TK2MSFTNGP12.phx.gbl...
> > You are correct on the raid levels and raid 10 is defined as a stripe of
> > mirrors. However Dell's documentation for the Perc3 and other
controllers
> > now states (and it's true) that their implementation of raid 10 is a
span
> of
> > mirrors. ie if you have a raid 10 of four 18GB disks and you create a
9GB
> > log file the file will wholy reside on the first mirror pair. The
second
> > mirror pair will not be used until the 1st mirror pair is full.
> >
> > This explains the dissappointing performance we have from our 22 disk
> > system. Although I benchmarked it, the one thing I did not do when I set
> it
> > up was to watch the disk lights.
> > For example our log file does indeed live on a 4 disk raid 10 array of
> 18GB
> > 15K drives. The log file is smaller than 18GB. When I/O occurs only two
of
> > the disk lights flash. The other two never flash. If it was true raid 10
> > then all 4 lights should flash as the i/o is striped.
> >
> > So I'm having to do the striping myself by spitting the files across
raid
> > arrays. ie Indexes on one, certain tables on another. Not a bad thing
> > anyway I guess. But if I'd known about dell's Raid 10 I'd have planned
> > differently. It's not east to make changes on a 24/7 system.
> >
> > An alternative with the dell perc3 would be to stripe the drives (Raid
0)
> > and then mirror using the O/S. Not one I care to choose.
> >
> > Paul
> >
> > http://docs.us.dell.com/docs/storage/perc3dc/ug/en/Levels.htm
> > The above document describes Raid 10 on the perc3/dc as a stripe of
> mirrors
> >
> >
> > http://docs.us.dell.com/docs/software/smarrman/marb32/ch8_perc.htm
> > This document shows that perc3/dc implements as a concatenation
> > Search for string "Supported RAID Levels for PERC Subsystem Controllers"
> >
> >
> >
http://docs.us.dell.com/docs/software/smarrman/marb32/ch3_stor.htm#1037893
> > This document describes spanned disks
> >
> >
> > "Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
> > news:uXdx2uZ6DHA.2952@.TK2MSFTNGP09.phx.gbl...
> > > Paul,
> > >
> > > Not sure what you mean exactly. The RAID numbers often get confusing
> when
> > > it comes to 1+0 or 0+1. One will be a stripe of mirrors and the other
> is
> > a
> > > mirror of stripes. The difference is mainly in the redundancy as the
> > stripe
> > > of mirrors will tolerate potentially more failures than a mirror of
> > stripes.
> > > In either case all the disks are used but you only get half the usable
> > disk
> > > space. That is how Raid arrays work. You sacrifice drives for
> redundancy
> > > and speed. I don't know why you say you need to split your files.
That
> > > should not be necessary.
> > >
> > > --
> > >
> > > Andrew J. Kelly
> > > SQL Server MVP
> > >
> > >
> > > "Paul Cahill" <XYZpaul.cahillXYZ@.blueyonder.co.uk> wrote in message
> > > news:eyHa3nY6DHA.2264@.tk2msftngp13.phx.gbl...
> > > > A word of warning. I discovered my expensive Dell Perc3/DC
controllers
> > > > implement Raid 10 as a span (concatenation) of mirrors not a stripe.
> > > > I have 22 disks and over half are idle.
> > > > I'm having to split the database file and log file into pieces.
> > > >
> > > > Paul
> > > >
> > > >
> > > > "Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
> > > > news:ucSRJy05DHA.2560@.TK2MSFTNGP09.phx.gbl...
> > > > > But she can't do a RAID 10 with just 3 drives. It's either a Raid
1
> > and
> > > > you
> > > > > loose a drive or Raid 5.
> > > > >
> > > > > --
> > > > >
> > > > > Andrew J. Kelly
> > > > > SQL Server MVP
> > > > >
> > > > >
> > > > > <sightdev@.yahoo.com> wrote in message
> > > > > news:9861f5eb.0401300736.6761b95d@.posting.google.com...
> > > > > > depends on your needs. If READ is the primary function, RAID5
> makes
> > > > > > sense because its less costly, but write is primary function
> > > > > > RAID10(0+1) is the best solution.
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>