Re: Poor raid 1 performance?

To make a long story short:

In news:43970b2c$1$3384$892e7fe2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx,
Folkert Rienstra va escriure:
>> And my (perhaps faulty) conclusion was that this represented a small
>> penalty (with respect to e.g. RAID 0,
>
> No, you said "non-Raid".

Okay, I found the origin of the misunderstanding.

I was specifically referring to RAID variations:
] The difference between RAID 0 and RAID 1 is the distance between one
stripe
] and the next on disk.

I made a little mistake while replying: I wrote
] [...] which should give a small penalty with respect to a non-RAID
] configuration (assuming media access is the bottleneck, that is).
I meant "non-RAID1" but did not make it clear. It clearly should have been
``contiguous reading'' (or plain ``RAID-0'' if you prefer), would have been
much clearer.
I am sorry for the mistake.

OTOH, I basically assumed a 1-sector stripe (which is not real.)
Or that the stripe size is lower than available free cache on the RAID
controller (and we hope so.)


> Read half of them, get half the throughput.

My point, exactly.
Since there is two drives, we end up at twice this throughput when data are
delivered to the main system by the RAID controller, and cannot make better
while reading sequencially.

If you compare to a non-RAID setup, RAID-1 might result in a better
throughput, for example if the connection link between the controller and
the drive is a limiting factor (ATA33 IIRC).

However, in the common case where the limiting factor is media access,
RAID-1 will result in about the same figures as non-RAID when seen from
outside (as you explained long and wide, thanks.)

OTOH, RAID-0 may deliver an higher throughput, because it can use more of
the available bandwidth on the connection link.


Antoine

.

Relevant Pages

  • Re: Onboard Raid (e.g. ICH10R) vs. Raid Controller card
    ... For Linux they are very reliable and fast. ... Also Softwre RAID removes the need for a spare controller. ... make sure to get a PCI-E (non-RAID) controller, ...
    (comp.sys.ibm.pc.hardware.storage)
  • Re: bad blocks on raid5 cause filesystem failure
    ... It is setup in in RAID 5. ... How could a RAID controller botch this up? ... should be rebuilt on spare drive if available from remaining drives. ... All is fine unless you have double fault. ...
    (comp.os.linux.hardware)
  • Re: on board RAID chip
    ... I don't actually want to use RAID, real or otherwise, ... the two IDE channels that the "raid" chip controls, ... 8212 Dual channel ATA RAID controller (PCI version seems to be IT8212, ... > harddrive over to the second channel and tried to boot. ...
    (Debian-User)
  • Re: Need to setup RAID in new hardware upgrade SBS2003
    ... I already moved the system to a new motherboard with an embedded Intel RAID ... controller a couple of months ago. ... did try but couldn't without wiping the drives first. ... install of the OS to get the RAID on the new board based on the Intel RAID ...
    (microsoft.public.windows.server.sbs)
  • Re: Dell PERC 2/SC Single Channel LVD SCSI RAID Controller
    ... host adapter with RAID control capabilities. ... PERC 2/SC is an ideal RAID solution for the internal ... Multiple logical drives/arrays per controller Up to 8 logical drives ...
    (uk.adverts.computer)