Re: Questions

[Adam Goryachev <mailinglists@websitemanagers.com.au>]

On 16/02/16 08:01, o1bigtenor wrote:
> On Mon, Feb 15, 2016 at 1:50 PM, Wols Lists <antlists@youngman.org.uk> wrote:
>> On 15/02/16 12:12, o1bigtenor wrote:
>>> I am looking at replacing ALL the drives in the array so that I can
>>> reduce the likelihood of these kind of issues for a longer period than
>>> a few months.
>>>
>>> Would you be able to tell me what steps should I be taking to replace
>>> the entire array?
>>>
>>> Should I replace the drives one at a time (sort of just like I did
>>> this time) using the same commands?
>> If you have a spare SATA (I presume they're sata drives) slot, then
>> definitely not. It might be worth buying an add-in card to give you an
>> extra slot, they're only a few quid.
>>
>> Look up "mdadm --replace". That'll keep the old drive in the array until
>> the new one has replaced it, keeping the array fully functional all the
>> time.
>>
>> Doing --fail, --remove, --add places the array in danger until the
>> entire sequence is complete, and if you're doing it several times then
>> you're massively increasing the chances of trouble.
>>
>> In fact, if you get an add-in card, you might be able to replace several
>> drives at once - I don't know - read up and see if it's supported (or not).
> Looked through well over a hundred different pages and only found 1 page
> that even hinted at what I am trying to do and details there were sparse.
>
> Read through the man page (likely one of the best for understandability that
> I have found so far) and it doesn't address the wholesale replacement of all
> the drives in an array. Most of the other pages that I found were what I would
> call old, ie before 2010, as I have found that all too often the software being
> discussed has changed and then the instructions given are not always useful,
> occasionally there is some value in these old pages but only sometimes.
>
> Most often the documentation was focused on replacing a faulty disc.
>
> This is NOT what I am proposing to do.
>
> I have a present working array and with to replace its components with the
> same size but new drives (which are NAS rated). Was thinking that using

I wanted to mention this, what drives do you have right now, and do know 
about SCT ERC?
Maybe start here (but you probably need to read more):
http://www.spinics.net/lists/raid/msg48199.html

Essentially, your current disks might be fine, but if you don't have the 
right settings, they could be "failing" regularly putting your data at 
risk. You should fix any issue here before you attempt to replace your 
drives.

> the fail remove and add process 4 seperate times might not be a good thing
> but I do not know of a different option. Compounding the difficulty is
> that there
> are no empty hard drive slots in the machine. I do have an external USB 3.0
> 2 drive holder that could be used.
>
> The only suggestion in all the documents I perused was to place spare drives
> into something like this external box and then add the drives into the array.
> The process was not laid out and leaves me with a number of questions.
>
> Is there a suggested method for replacing ALL the drives in an array (raid 10
> in this case)?

In order to replace all drives, I would suggest that you simply replace 
one drive 4 times (different drive each time).
The first question to ask, is your external USB drive bay reliable? If 
not, then there are other solutions that are probably less dangerous.

So, add your spare drive to the external USB drive bay, it should show 
up as /dev/sdy (for example)
Partition to match the rest of your existing drives
Add the new partition to your existing array: mdadm --manage /dev/md0 
--add /dev/sdx1
Replace one of the existing drives with the new one: mdadm /dev/md0 
--replace /dev/sda1 --with /dev/sdx1
Personally, because I distrust the external USB drive bay (don't ask me 
why, it just seems less reliable than internal sata), once the drive has 
finished being replaced, I would shutdown, remove the old drive, and 
install the replacement drive, then add another new spare, and repeat.

You can see this page for some extra information:
http://unix.stackexchange.com/questions/74924/how-to-safely-replace-a-not-yet-failed-disk-in-a-linux-raid5-array
> If I use the external box how do I do this (external box only holds 2 drives) so
> that I can transfer the information on the drives from the array to
> the new drives
> and then just replace the drives 2 at a time into the machine without
> there being
> issues because in the information transfer the drives will be sdg and
> sdh (AFAIK)
> and later they will be some of sdb, sdc, sde, and/or sdf.
I would suggest replacing one at a time.
> If one of the gurus on the list has an already prepared process list
> with the steps
> and commands that would be wonderful. I am thinking that this document would
> very much be appreciated by many others out there that are not on this list.
>
> TIA
>
>

Hope that helps.

Regards,
Adam

-- 
Adam Goryachev Website Managers www.websitemanagers.com.au