Re: 8203-E4A RAID5 vs. ASP protection

Hello Rob,

Am 01.03.2024 um 16:43 schrieb Rob Berendt <robertowenberendt@xxxxxxxxx>:

Chores are piling up but a google search (platform independent) shows a
line like: "...4 drives will give you more throughput than 3 as you’ll

be

striping reads across 3 drives rather than 2, so theoretically it should

be

as good as 50% faster."

Well, this is also true if you add even more disks. Five will give you
more throughput than four, and so on.

As far as I've understood RAID5, read performance is equal to a simple
stripe set, and it should be clear that three disks will outperform a
single disk, or even a mirror (RAID1). Writes can have multiple penalties:
Checksum calculation and writing, reading blocks from strips which aren't
in memory but are needed for checksum calculation, etc. As long as the
controller can keep up with the checksum calculation and disk contention
isn't achieved by the additional read and write traffic for handling
checksums as described above, I can't see why a three disk RAID5 is meant
to perform *particularly* bad.

What I'm after is: What is so special about "only three disks" giving
especially bad performance? And compared to what?

:wq! PoC



--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing list
To post a message email: MIDRANGE-L@xxxxxxxxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: https://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxxxxxxxx
Before posting, please take a moment to review the archives
at https://archive.midrange.com/midrange-l.

Please contact support@xxxxxxxxxxxxxxxxxxxx for any subscription related
questions.