Subject AW: [firebird-support] Re: Raid 0 or not ?
Author Steffen Heil
Hi

In RAID0 Reading ONE data block that is larger than the stripe size, (say
reading 5KB from a stripe set with 4kb stripes) forces both drives to spin
to the same position (as the data is distributed between them). If both
drives are idle anyway, they can do this at the same time, as can drives in
RAID1, no difference there.

However, if there are two concurrent reads of 5kb of different positions of
the file, you still force BOTH drives to visit BOTH places. In RAID1 is
suffices to habe one drive reading one section each. If the controller
implements serious read strategies, RAID1 might therefor read a lot faster
in multithreaded environments or environments where different positions of a
file need to be read consecutively. (as databases usually are - think of
multiple connections or index an data pages.)

In this setup even multi-drive RAID1 can really be an advantage.
Note however, that both setups slow down writes - while RAID0 also posses a
stability risk.
And even if you never see a full drive crash, a unreadable sector at the
wrong place might make your whole database crap, so RAID0 is a serious
treat.

Regards,
Steffen



-----Urspr√ľngliche Nachricht-----
Von: firebird-support@yahoogroups.com
[mailto:firebird-support@yahoogroups.com] Im Auftrag von svanderclock
Gesendet: Mittwoch, 18. November 2009 08:57
An: firebird-support@yahoogroups.com
Betreff: [firebird-support] Re: Raid 0 or not ?

Thanks nige !

so it's mean that my single file (the .gbd) will be split across all the
hard drive in raid0

But (speaking about read) is it not the same for RAID 1 ?
my data will be share across 2 disks, so to read it i can read simultaneous
in the disk 1 and in the disk 2 ? for write off course it's will be more
slower than raid 0 ?

also when we read the file, we read it mostly sequentially, bytes by bytes,
so doesn't really matter how many disk they are... no ?

thanks for all
stephane


--- In firebird-support@yahoogroups.com, "Nigel Weeks" <nweeks@...> wrote:
>
> Raid 0 is called striping. The '0' means it provides no redundancy or
fault
> tolerance.
>
> It divides the filesystem and files into blocks that you define when
> building the array, and then stores those blocks on consecutive hard
drives.
>
> Thusly, if you stored your 20GB file on a single SATA100 drive, you will
get
> a theoretical speed of 100MB/s data throughput
>
>
>
> Now, if you use RAID0 across multiple drives, say 6 * SATA100, and
depending
> on the interconnect you use (PCI, PCI-X, PCI-EX, PCI-EX4, PCI-EX8) you
can
> then get speeds nearing the throughput of your interconnect / bus system.
> This is because you essentially multiply the speed of each device by the
> number of devices you have (6 * 100MB/s = 600MB/s).
>
> Naturally, having 50 SATA drives hanging off one PCI slot will only get
you
> ~160MB/s, as that's the limit of the old style PCI bus.
>
>
>
> Here's one comparison of Interconnect methods
>
>
http://www.computerworld.com/computerworld/records/images/chart/pci_pcix.gif
>
>
>
> There may be inaccuracies in the above posting - I haven't had coffee
yet...
>
>
>
> Nige.
>
>
>
>
>
> From: firebird-support@yahoogroups.com
> [mailto:firebird-support@yahoogroups.com] On Behalf Of svanderclock
> Sent: Wednesday, 18 November 2009 8:36 AM
> To: firebird-support@yahoogroups.com
> Subject: [firebird-support] Re: Raid 0 or not ?
>
>
>
>
>
> I know but we are only looking for performance !
>
> For a Database of 20 GB, regarding the speed, is it better to use RAID 0
or
> not ? I read that read 0 is twice more faster BUT is it true when we speak
> about only one file (the .GDB) ?
>
> Thanks you by advance
> stephane
>
> --- In firebird-support@yahoogroups.com
> <mailto:firebird-support%40yahoogroups.com> , "Anderson Farias"
> <peixedragao@> wrote:
> >
> > Hi,
> >
> > |For a Database of 20 GB, regarding the speed, is it better to use RAID
0
> or
> > not ? I read that read 0 is twice more faster BUT is
> > |it true when we speak about only one file (the .GDB) ?
> >
> > I wouldn't use RAID 0 !! It would not be safe for your Database.
> >
> > RAID 1 is simple (cheap), safe and will also improve speed for your
reads.
>
> > I've been using it with great results.
> >
> > Also, If you can afford and need something even more "secure" than you
may
>
> > want to try RAID 10.
> >
> >
> > Regards,
> > Anderson
> >
>
>
>
>
>
> [Non-text portions of this message have been removed]
>




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