Weblog entry #375 for simonw
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#375
dd if=/dev/urandom of=/dev/sdc
Posted by simonw on Sat 10 Jul 2010 at 00:48
That'll have to do, since I doubt the warranty will be honoured if I have smashed the platters. 640GB drive going back to Tesco's. Has a fault, claims to write data fine, but has a load of bad blocks which are only apparent on attempting to read them. Fortunately I spotted this before losing any important data, guess I should have run bad blocks on the whole disk before using it at all, and that wouldn't find blocks that turn bad.
Since this drive is exclusively used for (personal) data backup I wondered if there was a way to persuade the replacment USB external drive to do some sort of read after write verification. As otherwise it is rsync checksums and tar -w, and whatever other commands I use for backup, and these almost all do more IO than is needed to ensure the data is safe. And "find . -type f -print0 | xargs cat >/dev/null" is rather a crude test for readability.
In the days of tape backup many devices had a read head after the write head, allowing it to immediately establish that the data was readable.
How are your backups verified?
Since this drive is exclusively used for (personal) data backup I wondered if there was a way to persuade the replacment USB external drive to do some sort of read after write verification. As otherwise it is rsync checksums and tar -w, and whatever other commands I use for backup, and these almost all do more IO than is needed to ensure the data is safe. And "find . -type f -print0 | xargs cat >/dev/null" is rather a crude test for readability.
In the days of tape backup many devices had a read head after the write head, allowing it to immediately establish that the data was readable.
How are your backups verified?
Comments on this Entry
Posted by Anonymous (217.216.xx.xx) on Sat 10 Jul 2010 at 01:11
Mostly praying.
[ Parent | Reply to this comment ]
How are your backups verified?
They are tested - more often than I would like but probably not as often as I should.
--
"It's Not Magic, It's Work"
Adam
[ Parent | Reply to this comment ]
I think verification is distinct from testing.
Testing shows that if the backup worked, it can be restored.
Verification is showing the backup worked.
Now sure testing is a form of verification, but unless you test every backup - sods law says.....
My thinking all stems from silent write error in backups to disk. Not something that use to happen with SCSI tape devices because they do read after write verification.
Testing shows that if the backup worked, it can be restored.
Verification is showing the backup worked.
Now sure testing is a form of verification, but unless you test every backup - sods law says.....
My thinking all stems from silent write error in backups to disk. Not something that use to happen with SCSI tape devices because they do read after write verification.
[ Parent | Reply to this comment ]