Re: Faster Disk Recovery ??
From: Walter Mautner (nownews.10.eatallspam_at_spamgourmet.com)
Date: 08/11/04
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Date: Wed, 11 Aug 2004 00:14:08 +0200
don_pettengill@spamgilent.com wrote:
> I've been having my own problems lately. My HD developed a few glitches
> and I lost some unknown files after fsck (day before I went on vacation,
> "of course").
>
> Not to worry; I have reasonable backups. I keep an rsync'd mirror on a
> USB disk, which is a week or two old and updated nightly with a cpio
> arcive of changed files.
>
> Complaints:
>
> *) This is a 120GB IDE disk. Running fsck -c -c (to updated the bad
> block list) took over 24 hours. Wow!
>
Most probably the disk does have bad sectors. What happens, is
- multiple retries to read (by the disk hardware controller) for every
defective sector
- "lost interrupt" or similar in dmesg, followed by ide bus resets and dma
being turned off for that disk/controller path, further slowing down the
system. Similar things happen with usb.
I had a 80GB Maxtor drive die on me a few days ago, showing (once again, my
stack of half or full defective drives grows) similar symptoms. Windows
booted but froze with steady drivelight soon afterwards, and linux
complained but kept running "degraded" thanks raid1.
.....
>
> 1) Anyone know what speed protocol Knoppix uses for USB2 disks? Is it
> by default the faster ehci or is it the usb1 uhci? If the latter by
> default can it be changed by fiddling with modules as above?
> I will run some tests when next my system can be spared .....
>
ehci or ohci should get the higher speed, unless the drive has troubles.
> 2) Given that one generally has just one big IDE disk in a system -
> assuming no master/slave which I don't like - how the #$!! can one
> recover that disk quickly? A bare metal recover from USB2 disk doesn't
> look feasible at all. Am I really reduced to ripping out the drives and
> going to a spare system for a quicker copy? My wife already complains
> about the computers lying aroung - now I will have to have a spare open
> chassis too :-) I have a SCSI controller and 1/more SCSI disks in there
> but the boot priorities relegate these to backups at the moment.
>
Since it isn't the first high capacity drive that died on me, I resort to
linux software raid, keeping each partition raid1 except swap (two
partitions no raid because the kernel does it automagically) and /tmp on
raid0 for speedup.
My two ide drives are both slave, with dvdrom and cdrw on the master
positions, thanks to limited length of cabling. There is no loss in speed
at all:
/dev/hdb6:
Timing buffer-cache reads: 1276 MB in 2.00 seconds = 637.14 MB/sec
Timing buffered disk reads: 148 MB in 3.02 seconds = 49.03 MB/sec
[Die Aug 10 23:56 /home/walter]# hdparm -tT /dev/hdd6
/dev/hdd6:
Timing buffer-cache reads: 1276 MB in 2.00 seconds = 637.78 MB/sec
Timing buffered disk reads: 166 MB in 3.02 seconds = 54.99 MB/sec
/dev/md0: (hdb6/hdd6)
Timing buffer-cache reads: 1268 MB in 2.00 seconds = 633.15 MB/sec
Timing buffered disk reads: 166 MB in 3.00 seconds = 55.32 MB/sec
with md0 the / partition.
You can use cheap but fast udma133 drives, and for less valuable or
regularly backuped data you can double partition capacity by using stripe
(raid0).
> 3) What are other regular Joes doing for backup/recovery? Many systems
> must easily have tens of GB of data to roll over. But I am now on day 3
> of my system recovery (end in sight thank goodness). If I thought there
> was a better backup method I might do it some other way. Perhaps an
> rsync over the network to a mirror disk, in an IDE caddy (I already use
> those quite a bit). In that case just switching caddies would do it,
> possibly also with some incremental cpio backup. But I had hoped to
> avoid having another whole system blazing away just for backups. That's
> what i liked about the USB case (for the IDE drives) - just plug in,
> back up, and unplug. But if the transfer speed sucks - and it did big
> time in default Knoppix recovery - it isn't practical. BTW, disk images
Maybe knoppix doesn't utilize dma on the source (ide) drive by default (you
will have to use hdparm -d 1 /dev/hdX), or it will be turned off soon after
stumbling across the first bad sectors.
...
> I see lots of questions on the net about "convenient bare-metal
> recovery", but so far I never saw any good answer. Maybe there isn't
> one.
>
Mmhm, external usb or firewire drives have their advantages but also
pitfalls. Recently I tried to backup a laptop on such a drive, via a pcmcia
firewire card - got stuck after one or two minutes in windows, with "drive
unavailable" message. Same thing with the usb2 port. Oh, damned, the pcmcia
card shared its irq with a wlan card, the ac97 onboard sound and something
else I forgot. Not even disabling the devices in device manager did help
(and the bios didn't allow for anything on that laptop). Just using plain
old built-in usb1.1 worked slow, but it copied the whole stuff.
> BTW, tapes are out (slow/small/sequential access sucks, for anything *I*
> can afford). I could see DVD data backups but we quickly get into the
> "10-DVD backup set" even at 4.7GB per disk; it just isn't practical.
Now if we are speaking scsi, a dlt drive might do the trick (40/80GB).
However, it isn't *that* fast.
Tape backups still have their advantages!
....
> "There are two kind of computer user: Those who have lost data; and
> those who are going to".
>
Take care and raid :)
-- Longhorn error#4711: TCPA / NGSCB VIOLATION: Microsoft optical mouse detected penguin patterns on mousepad. Partition scan in progress to remove offending incompatible products. Reactivate your MS software. Linux woodpecker.homnet.at 2.6.8-rc2-bk9pkt [LinuxCounter#295241]
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