Re: MDADM RAID1 of external USB 3.0 Drives
Linux-Fan <Ma_Sys.ma@web.de> writes:
> On 09/27/2014 09:52 PM, lee wrote:
>> Linux-Fan <Ma_Sys.ma@web.de> writes:
>>> On 09/22/2014 03:23 AM, lee wrote:
>>>> Linux-Fan <Ma_Sys.ma@web.de> writes:
>>>>> On 09/21/2014 08:41 PM, lee wrote:
>>>>>> Linux-Fan <Ma_Sys.ma@web.de> writes:
>>>>>>>> On 09/20/2014 04:55 PM, lee wrote:
>>>>
>>>> I've seen the smart info show incredible numbers for the hours and for
>>>> the temperature. Hence I can only guess which of the values are true
>>>> and which aren't, so I'm simply ignoring them. And I never bothered to
>>>> try to relate them to a disk failure. When a disk has failed, it has
>>>> failed and what the smart info says is irrelevant.
>>>
>>> I always at least try to read/interpret the SMART data. I consider it
>>> valuable information, although it is sometimes difficult to interpret.
>>> (Especially Seagate's Raw Read Error Rate and some other attributes).
>>
>> How do you know which of the numbers are correct and which aren't?
>
> I always check whether they are plausible. I have recorded my computer
> usage times and the oldest disk has always been in use. My computer
> usage times sum around the same as the disk "power-on" and they increase
> on a daily basis which makes me believe the data is correct. For
> temperature, it gives me weird results which either means they are in
> Farenheit or just wrong which is why I am ignoring that data at the
> moment. Other potentially "bad" things are all zero which I read as
> "SMART has nothing bad to report" etc.
So do these values actually tell you? Is there a difference in usage
times between a disk that has been busy with seeking and
writing/receiving data all the time --- like when rebuilding a RAID ---
and another disk that has been (mostly) idling all the time?
When you are seeing incredible values for the temperatures, does this
tell you that other values you're seeing are more or less incredible?
> Well, but SATA and USB are the only means to connect my HDDs which are
> available in the newest system. Older systems also have IDE but I do not
> trust it to be more reliable than SATA. Also, I have never experienced a
> single loss of connection or anything with SATA.
I've seen it.
SAS is probably more reliable than SATA because it's designed to be.
It's an interesting question ...
>> RAID isn't exactly non-complex. And what's more complex: RAID with LVM
>> with ext4 or btrfs without LVM and without RAID because it has both
>> built-in? You can eliminate a hardware RAID controller which can fail
>> and has the disadvantage that you need a compatible controller to access
>> your data when it does. You can also eliminate LVM.
>
> MDADM + EXT4 combines the both technologies I know best of these
> mentioned above, which is why I chose to go this way. So far, the
> complexity of an "internal" RAID configuration has not been an issue to
> manage while the "external" RAID took an additional parameter in an
> initscript to work correctly.
Try to look a bit beneath the surface you're seeing. The complexity is
mostly hidden from you, which can be nice as long as everything works as
you want it to. Once it doesn't, the complexity can drown you.
>> What's more reliable?
>
> I cannot tell which is why I chose the one I found most simple to setup
> and maintain.
I don't know either --- I only know that what appears to be the most
simple solution isn't necessarily the most simple or best one and that
the most simple solution which reliably does what you want it to do is
usually much better than a less simple solution.
>> Using the disks for VMs? That's all the more reason to have a server?
>
> Well, unlike with "server usage" I normally only run one or two VMs at
> the same time (not enough RAM could be one of the reasons) while having
> many different images on my HDDs for testing and learning purposes.
Well, the setup doesn't sound bad at all, in theory.
Not enough RAM? Do you have only 4GB?
>> Remember the above mouse problem: These computers are awfully slow, so
>> perhaps they forget about the mouse. Now put some good load on yours
>> and see what happens to your USB disks ...
>
> I will try to reproduce such a mouse or keyboard issue first because
> that seems easier to do and requires less preperation in terms of backup
> (I will do it on a dedicated testing machine).
Hm, interesting :) I wouldn't know how to reproduce it. One of the
major slowdowns on this machine seems to be graphics. Perhaps I need to
look into using an appropriate driver for the graphics card. The latest
version of Libreoffice (4.x, not the ancient one that's in Debian) might
be somehow involved in this. Take a spreadsheet with like 2000 rows,
apply some filters, mark all the lines displayed and you are kinda stuck
because the machine is too slow to let you do something, like going into
the Edit menu to copy what's selected. You have to be extremely patient
then ...
>>> Otherwise, I backup important data (which is luckily not that much) to
>>> 16 GB CF cards formatted with FAT32 (I have taken measures to keep
>>> UNIX file permissions and special files like FIFOs etc. intact).
>>
>> CF cards? FAT32? Do you have a good idea of how reliable this is?
>
> I have had a Windows 95 FAT system from 1996 and it still worked.
That's amazing! I tried out W95 when I was looking for an alternative
to OS/2. It lasted about half a day before it had rendered itself
unusable beyond repair, so I decided to use Linux.
Anyway, did you run chkdsk sometimes?
> I trust the CF cards to be my most reliable means of storage because
> they do not contain mechanical parts, use SLC chips (my failed SSD was
> using MLC) and are specified for some extended temperature ranges as
> well as some shock resistance.
At least there seems to be some agreement that they do better than SD
cards. Some time, I might even buy an SSD ...
> In terms of file systems, FAT32 is rather simple.
It's also great at losing data.
> And rather than any "data-format" failing, I always worry about the
> programs failing (or going missing) to read the data when it is
> necessary.
Failing in which way? The data being so old that the software which was
used to create it isn't available anymore?
> Still, I also think about using an EXT-based system and checking if
> any Windows programs exist to read them (I have read about, but not
> tried ext2fsd yet).
IIRC, I've read about something to use ext3 with Windows. But Windows
is a dead end.
>> My experience with FAT is that it is bound to fail sooner than later. I
>> never used a CF card, only SD cards, though not much. I haven't seen an
>> SD card failing yet.
>
> The only flash memory which I have seen failing were cheap USB sticks
> and my SSD. Also, I have heard about cheap SD cards failing. My CF cards
> have never failed. (But my HDDs have also never failed yet. :) )
Hm, I have a 1GB USB stick which is about 7 years old. It still works
(probably because it was almost never used). It's falling apart,
though. I really should get one with more capacity so I don't need to
burn a Gentoo DVD ...
And there seems to be some agreement that CF cards work better than SD
cards. But who knows, perhaps they improved the SD cards.
--
Knowledge is volatile and fluid. Software is power.
Reply to: