[LUAU] SATA hot swap - off topic

Brian Chee chee at hawaii.edu
Wed Jul 7 15:51:47 PDT 2004


Take a hard look at the hotswap cages from supermicro....inexpensive and
they have the special connectors where the ground lines are longer and mate
first and demate last...this makes sure that the drives dont' get hit by a
capacitance charge during the hotswap process....this is the major reason
why hotswap cages are so expensive from "brand names"....the other thing
that these guys do is during the hotswap process it sends a signal to the
controller(s) that a demate is in progress and aquiesces the drive in
question.  This is why controllers like the Adaptec and the 3Ware are quite
a bit more expensive than controllers like the promise.

That and dedicated RAID processors....the DAC-960's that I use (ultra 160
scsi) have a dedicated i960 processor and battery backed ram just to handle
raid functions...this is why linux sees the volume as a single drive, not
multiple drives. It also dramatically reduces system overhead, since
controllers like the promise offload RAID functions into the main CPU,
whereas the 3Ware and the Adaptec do the processing in buss disconnect mode;
thusly not drawing down the system buss for RAID functions. THis is also why
stripe set rebuilds don't affect the system on such cards too.

/brian chee



University of Hawaii ICS Dept
Advanced Network Computing Lab
1680 East West Road, POST rm 311
Honolulu, HI  96822
808-956-5797 voice, 877-284-1934 fax

----- Original Message ----- 
From: "Vince Hoang" <vince.hoang at gmail.com>
To: "Linux/Unix Advocates/Users Hawaiian community discussion list"
<luau at lists.hosef.org>
Sent: Wednesday, July 07, 2004 11:34 AM
Subject: Re: [LUAU] SATA hot swap - off topic


> On Wed, 07 Jul 2004 00:19:54 -1000, Jeff Mings <jeffm at lava.net> wrote:
> > Thanks for the suggestion.  What I'd really like to be able to do is
> > just switch out backup hard drives once a month.  The goal is simple
> > data redundancy, not hardware fail-over.  I'm planning on colocating a
> > server, and I was hoping I could just umount /dev/whichever ,  unlock a
> > drive tray, and reverse the process for a different drive.  It just
> > sounds too easy, though.
>
> You can use hdparm to quiesce the bus. Your version of hdparm support
> hotswap, but no guarentees if your kernel does.
>
> http://www.redhat.com/archives/fedora-test-list/2004-March/msg01204.html
>
> Even if it does work for your kernel, I have to advise against your
> approach, because hotswap != removable storage. If you have wiggle
> room in the colo space, give firewire a fair chance.
>
> > MonMotha wrote:
> > > This is mostly useful on RAID arrays though.  See the raidhotadd and
> > > raidhotremove (or is it raidhotdel?) commands.
>
> I believe this only tickles the md driver and not the bus.
>
> -Vince
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