External USB2.0 HDD disconnect

[Madison Kelly]

Hi Lennart,

   Thanks for the reply and the confirmation of what I thought... On the 
removeable tray; it isn't an internal removeable tray, it's an external 
USB2.0-attached housing that accepts removeable hdd trays. I like it 
because it will make it as easy as possible for the client to swap out 
the carriers (no [un]plugging the chassis) and the hdd tray is as small 
as possible when using a full hdd for backup.

   I guess the next step then is to make a manual backup, put the server 
into init 1 and then change all the filesystems to LVM... -Shoul- be 
easy enough... (I know, why don't I just kick Murphy in the arse and see 
if he leaves me alone still, too! ;) ).

Madison

Lennart Sorensen wrote:
> On Tue, Jan 20, 2004 at 01:33:51PM -0500, Madison Kelly wrote:
> 
>>Hi all,
>>
>>  I am looking into alternatives to tape backup after my last little 
>>fiasco and I am ready to settle on an external USB2.0 chassis with 
>>removeable HDD carrier trays. Now, I know that with other USB devices 
>>like digital cameras and keychain memory sticks I can dismount and then 
>>physically disconnect the filesystem from the machine while the computer 
>>is on. I am *assuming* I can do that with an external HDD chassis as 
>>well but I thought I best turn to TLUG for sage advice lest I be greated 
>>by the humbling effect ;).
> 
> 
> A USB HD chassis should work.  Just remember that you disconnect the USB
> after you umount the drive (if mounted), or making sure the disk is
> sync'd.  The USB boxes are pretty cheap now as far as I know.  The HDD
> removable trays never made any sense to me, and can only be removed
> safely while powered off (or disconnected in the case of USB).
> 
> 
>>  Any experiences/comments/horror stories?
>>
>>Madison
>>
>>PS - My plan is to use drives the same size as the server and to have a 
>>script mount the drive and then 'dd' the server's data to the backup 
>>hard drive thereby hopefully allowing for baremetal recovery if it 
>>becomes so needed in the future. Do I need LVM/snapshot to ensure data 
>>consistency or is 'dd' sufficient so long as the users are gone for the day?
> 
> 
> If after dd reads block 10000 something goes and changes block 5000, it
> won't be in the backup.  If something changes a filesize and appends
> some data to a file stored at location 20000, you will still get the
> data in dd, but the metadata changes will be missed since they are near
> the start of the disk.  dd is NOT how to backup a filesystem that is in
> use.  LVM snapshots on the other hand can do a atomic snapshot that
> should be as valid as the machine is at that point (same as if it had
> instantly lost power at that point).  Databases should recover although
> perhaps won't be 100% happy about life.
> 
> Lennart Sorensen


--
The Toronto Linux Users Group.      Meetings: http://tlug.ss.org
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://tlug.ss.org/subscribe.shtml