Re: [smartmontools-support]raid5 slower than raid1

[Andreas U. <un...@ne...>]

(offtopic):

Writing to RAID5 is slower then to RAID1. While RAID1 is simply 
mirroring beetween the
disks, RAID5 needs to calculate a checksum which is written to all disks 
(not like RAID4
where you only have one parity disk) in addition to the data.

I have seen some "old" scsi raid controllers, where also reading from 
RAID5 can be much
slower then RAID1, because they have a bad algorithm to read the data 
from several disks
and link them together.

But often this behaviour can be changed through firmware updates.

Cheers,
Andreas

Hunter Peress wrote:

> Maybe you can help me with some performance issues?
>
> This is hdparm -Tt on a 2x36GBx10k
>
> Timing cached reads:   796 MB in  2.00 seconds = 398.00 MB/sec
> Timing buffered disk reads:   96 MB in  3.03 seconds =  31.68 MB/sec
>
> and on a   4x18GBx15k
> Timing cached reads:   924 MB in  2.00 seconds = 462.00 MB/sec
> Timing buffered disk reads:   90 MB in  3.03 seconds =  29.70 MB/sec
>
>
>
> The raid5 should be a heck of a lot faster no?
>
> both have aka compaq integrated smart controller
> cardinfo:RAID bus controller: LSI Logic / Symbios Logic 53C1510 (rev 02)
>
>
>
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> Hunter Peress
> hp...@sf...
> Web Programer
> The Santa Fe New Mexican, Inc.
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