Re: HDD vs. RAID (was Re: Lilo Q)
On Mon, 2002-06-10 at 08:46, Ian D. Stewart wrote:
> On 2002.06.10 03:35 Anthony DeRobertis wrote:
> > On Sun, 2002-06-09 at 20:33, Alvin Oga wrote:
> >
> > > if you have a nearly full 80GB disks ... it wont matter
> > > if you have 1x 80GB or 4x 20GB( stripping )
> >
> > No, it does matter. You can expect at least one of four 20GB drives to
> > fail much sooner than one 80GB drive, assuming same MTBF numbers on
> > all
> > drives.
> >
> > The MTBF for one 50,000hr MTBF disk is 50,000hr. For four of them, it
> > is
> > 13,500Hr.
> >
> > [ And, if you operate the four for a year, you can expect 1 to fail. ]
>
> So then, the primary advantages of RAID are access speed and data
> redundancy and the primary advantage of a stand-alone HDD is
> reliability?
Well, redundancy is one way of ensuring reliability, so your
statement is slightly off.
The problem with JBODs (just big ole disks, i.e. single disks)
is that all of your eggs are in one basket. Even though the
MTBF is 50,000 hours, the M in MTBF is, of course Mean, so
even though it should last 50,000 hours, it _might_ puke tomorrow.
So, use RAID[145] (or better yet: RAID1+0) just so you are spreading
the risk...
Another point that may have already been mentioned: with a JBOD,
you only have one spindle, so the read-write heads can only be
at 1 place at a time. With RAID solutions, the read-write heads
will be in as many different places at once as you have disks.
Note, though, that since the CPU overhead from calculating RAID[45]
recovery blocks necessitates a caching controller. Otherwise,
write speeds will be slower.
--
+---------------------------------------------------------+
| Ron Johnson, Jr. Home: ron.l.johnson@cox.net |
| Jefferson, LA USA http://ronandheather.dhs.org:81 |
| |
| "I have created a government of whirled peas..." |
| Maharishi Mahesh Yogi, 12-May-2002, |
! CNN, Larry King Live |
+---------------------------------------------------------+
--
To UNSUBSCRIBE, email to debian-user-request@lists.debian.org
with a subject of "unsubscribe". Trouble? Contact listmaster@lists.debian.org
Reply to: