How important is SCTERC?

How important is SCTERC?

[Ram Ramesh]

Experts,

I ordered a couple of 6TB drives from goHarddrive that claimed to be NAS 
suitable, but SMART shows that they do not support
scterc. I want to replace two of my 3TB drives with these in mdadm 
raid6. I can get a replacement or return, but want to avoid the hassle, 
if I am not seious danger.

I do run tler.sh that sets 180s timeout for drives that do not have 
scterc from /etc/rc.local. Am I putting my data in serious danger? I 
only have videos and tv recordings in this md which can be replaced with 
significant effort (about 12TB of movies and tv shows will take some 
time to copy from my DVDs/BDs)

Ramesh

Re: How important is SCTERC?

[Phil Turmel]

On 04/27/2017 11:35 PM, Ram Ramesh wrote:
> Experts,
> 
> I ordered a couple of 6TB drives from goHarddrive that claimed to be NAS
> suitable, but SMART shows that they do not support
> scterc. I want to replace two of my 3TB drives with these in mdadm
> raid6. I can get a replacement or return, but want to avoid the hassle,
> if I am not seious danger.

Depends on "serious".  I would return for exchange with proper NAS
drives.  And report the vendor for false advertising.

> I do run tler.sh that sets 180s timeout for drives that do not have
> scterc from /etc/rc.local. Am I putting my data in serious danger? I
> only have videos and tv recordings in this md which can be replaced with
> significant effort (about 12TB of movies and tv shows will take some
> time to copy from my DVDs/BDs)

The 180-second timeout is a band-aid, not a solution.  Keep in mind that
your array will appear to be frozen for up to three minutes any time you
have a URE.  That will have application side-effects and especially
consequences from impatient users.

Phil

Re: How important is SCTERC?

[Peter Grandi]

> [ ... ] I do run tler.sh that sets 180s timeout for drives
> that do not have scterc from /etc/rc.local. Am I putting my
> data in serious danger?

No.

> I only have videos and tv recordings in this md

The problem with SCT/ERC absence is that the 2-3 minutes of
retries suspend IO for that long, and for people running
interactive applications (usually LAMP-style web applications)
that is a bad idea, but in your case you seem to have just a
personal archive of entertainment files.

For interactive "enterprise" applications the common practice is
to reduce the error timeout to 1-2 seconds, so the failing drive
drops out of the MD set quickly and can be replaced, minimizing
delays.

> which can be replaced with significant effort (about 12TB of
> movies and tv shows will take some time to copy from my
> DVDs/BDs)

Backups are very important, and RAID is not an alternative to
backups. You can buy and use SMR disk drives as if they were
tapes (or with a filesystem like NILFS2) to do that backup, and
they are quite cheap.

Re: How important is SCTERC?

[Ram Ramesh]

On 04/28/2017 07:18 AM, Phil Turmel wrote:
> On 04/27/2017 11:35 PM, Ram Ramesh wrote:
>> Experts,
>>
>> I ordered a couple of 6TB drives from goHarddrive that claimed to be NAS
>> suitable, but SMART shows that they do not support
>> scterc. I want to replace two of my 3TB drives with these in mdadm
>> raid6. I can get a replacement or return, but want to avoid the hassle,
>> if I am not seious danger.
> Depends on "serious".  I would return for exchange with proper NAS
> drives.  And report the vendor for false advertising.
>
>> I do run tler.sh that sets 180s timeout for drives that do not have
>> scterc from /etc/rc.local. Am I putting my data in serious danger? I
>> only have videos and tv recordings in this md which can be replaced with
>> significant effort (about 12TB of movies and tv shows will take some
>> time to copy from my DVDs/BDs)
> The 180-second timeout is a band-aid, not a solution.  Keep in mind that
> your array will appear to be frozen for up to three minutes any time you
> have a URE.  That will have application side-effects and especially
> consequences from impatient users.
>
> Phil

I am quite unhappy with the vendor and wanted to make sure that I am not 
overreacting. Thanks. I have started the return process. Hopefully, that 
is all there is to it.

Ramesh

Re: How important is SCTERC?

[Ram Ramesh]

On 04/28/2017 08:07 AM, Peter Grandi wrote:
>> [ ... ] I do run tler.sh that sets 180s timeout for drives
>> that do not have scterc from /etc/rc.local. Am I putting my
>> data in serious danger?
> No.
>
>> I only have videos and tv recordings in this md
> The problem with SCT/ERC absence is that the 2-3 minutes of
> retries suspend IO for that long, and for people running
> interactive applications (usually LAMP-style web applications)
> that is a bad idea, but in your case you seem to have just a
> personal archive of entertainment files.
>
> For interactive "enterprise" applications the common practice is
> to reduce the error timeout to 1-2 seconds, so the failing drive
> drops out of the MD set quickly and can be replaced, minimizing
> delays.
Interestingly, the drives did not pass SMART test and mkfs.ext4 -c -c  
checks. So, I returned them. I plan to buy WD gold (the other extreme in 
price point :-)
>
>> which can be replaced with significant effort (about 12TB of
>> movies and tv shows will take some time to copy from my
>> DVDs/BDs)
> Backups are very important, and RAID is not an alternative to
> backups. You can buy and use SMR disk drives as if they were
> tapes (or with a filesystem like NILFS2) to do that backup, and
> they are quite cheap.
I am using my actual DVDs as backup. For TV shows they are available in 
Netflix, if I really want to watch them again.
However, your point is well taken. I will think about backup as my 
collection has grown over the years and it will be really a pain to go 
back to DVDs to populate my media server.
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