[CentOS] Disaster recovery recommendations

Sat Oct 31 21:34:08 UTC 2015
Nux! <nux at li.nux.ro>


What you're describing sounds like "ddrescue" which is free and open source.

It's in EPEL.

Sent from the Delta quadrant using Borg technology!


----- Original Message -----
> From: "Mark LaPierre" <marklapier at gmail.com>
> To: centos at centos.org
> Cc: "Mark LaPierre" <marklapier at aol.com>
> Sent: Saturday, 31 October, 2015 20:30:54
> Subject: Re: [CentOS] Disaster recovery recommendations

> On 10/31/15 15:17, Valeri Galtsev wrote:
>> On Fri, October 30, 2015 9:31 pm, Mark LaPierre wrote:
>>> On 10/30/15 17:30, Max Pyziur wrote:
>>>> Greetings,
>>>> I have three drives; they are all SATA Seagate Barracudas; two are
>>>> 500GB; the third is a 2TB.
>>>> I don't have a clear reason why they have failed (possibly due to a
>>>> deep, off-brand, flakey mobo; but it's still inconclusive, but I would
>>>> like to find a disaster recovery service that can hopefully recover the
>>>> data.
>>>> Much thanks for any and all suggestions,
>>>> Max Pyziur
>>>> pyz at brama.com
>>> If you can get them mounted on a different machine, other than the one
>>> with the problem mother board, then I suggest giving SpinRite a try.
>>> https://www.grc.com/sr/spinrite.htm
>> I listened to guy's video. Pretty much sounds like what command line utility
>> badblocks
>> does. The only viable I hear is its latest addition when this utility
>> flips all bits and writes into the same location. In fact it is anything
>> (containing both 0's and 1's) that is to be written to the sector, then on
>> write the drive firmware kicks in as the drive itself on write operation
>> reads written sector and compared to what was sent to it and if it differs
>> it labels sector, or rather block I used wrong term just after this guy as
>> I was listening while typing. Anyway this forces discovery and
>> re-allocation of bad blocks. Otherwise bad blocks are discovered on some
>> read operation, if CRC (cyclic redundancy check sum) on read doesn't
>> match, the firmware reads the block many times and superimposes the read
>> results, if it finally gets CRC match it happily writes what it came with
>> to the bad block relocation area, and adds block to bad block
>> re-allocation table. After some number of reads if firmware doesn't come
>> up with CRC match it gives up, writes whatever superimposed data is. So
>> these data are under suspicion as even CRC match doesn't mean the data is
>> correct. This is why there are filesytems (ZFS to name one) that store
>> really sophisticated checksums for each of files.
>> Two things can be mentioned here.
>> 1. If you notice that sometimes the machine (I/O actually) freezes on
>> access of some file(s), it most likely means the drive firmware is
>> struggling to do its magic on recovery of content and re-allocation of
>> newly discovered bad blocks. Time to check and maybe replace the drive.
>> 2. Hardware RAIDs (and probably software RAIDs - someone chime in, I'm
>> staying away from software RAIDs) have the ability to schedule "verify"
>> task. This basically goes over all sectors (or blocks) of all drives thus:
>> a. forcing drive firmware to discover newly developed bad blocks; b. as
>> drives when working on badblock will often time out, then RAID firmware
>> will kick this drive out, and will start rebuilding RAID, thus re-writing
>> content of bad block on the drive developed bad block. In this case the
>> information comes from good drives, thus less likely to be corrupted. What
>> I described is best case scenario, not always drive will time out... so
>> even hardware RAIDS are prone to actual data corruption, Bottom line, it
>> is good to migrate to something like ZFS.
>> Thanks.
>> Valeri
>>> It's inexpensive which makes it a low risk and not much of a loss if it
>>> doesn't work.
>>> Also consider this a lesson learned.  The cost of a second low capacity
>>> machine, including the electric bill to run it, is insignificant
>>> compared to paying for data recovery.
>>> http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=7841915&Sku=J001-10169
>>> If you insist on keeping personal control of your data, like I do, then
>>> that is the best way to go about it.  Use the second machine as your
>>> backup.  Set it up as a NAS device and use rsync to keep your data
>>> backed up.  If you're paranoid you could even locate the old clunker off
>>> site at a family/friend's home and connect to it using ssh over the
>>> internet.
>>> Your other option is to use a cloud storage service of some kind.  Be
>>> sure to encrypt anything you store on the cloud on your machine first,
>>> before you send it to the cloud, so that your data will be secure even
>>> if someone hacks your cloud service.  There's another drawback to using
>>> a cloud as your backup.  The risk is small, but you do have to realize
>>> that the cloud could blow away along with your data.  It's happened
>>> before.
>>> --
>>>     _
>>>    °v°
>>>   /(_)\
>>>    ^ ^  Mark LaPierre
>>> Registered Linux user No #267004
>>> https://linuxcounter.net/
>>> ****
>>> _______________________________________________
>>> CentOS mailing list
>>> CentOS at centos.org
>>> https://lists.centos.org/mailman/listinfo/centos
>> ++++++++++++++++++++++++++++++++++++++++
>> Valeri Galtsev
>> Sr System Administrator
>> Department of Astronomy and Astrophysics
>> Kavli Institute for Cosmological Physics
>> University of Chicago
>> Phone: 773-702-4247
>> ++++++++++++++++++++++++++++++++++++++++
>> _______________________________________________
>> CentOS mailing list
>> CentOS at centos.org
>> https://lists.centos.org/mailman/listinfo/centos
> Hey Valeri,
> What you say is true and should be considered when he rebuilds his system.
> The point of my post was to suggest a way for the OP to recover his data
> at a reasonable cost using Spinrite.
> One point you may be confused with is that Spinrite does not care what
> file system you have on your disk.  Spinrite does not mount the file
> system.  It access the disk storage media one sector at a time using the
> actual drive hardware/firmware to read the data from each sector.  If it
> does not succeed in reading the sector it keeps trying using various
> methods until it gets a read or until it is satisfied that the sector is
> unreadable.
> When it gets a read it writes it back to the center of the track where
> it's supposed to be and checks to be sure that it worked by reading it
> back again.
> As Spinrite progresses across the storage media the drive firmware
> manages the marking of truly unrecoverable sectors as bad and the other
> sectors as good.
> --
>    _
>   °v°
>  /(_)\
>   ^ ^  Mark LaPierre
> Registered Linux user No #267004
> https://linuxcounter.net/
> ****
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