Very Large Filesystems

In article . com,
Aknin wrote:
On May 1, 3:15 am, Ernst S Blofeld
wrote:
Jan-Frode Myklebust wrote:
Is there any other solution than backups, if neither the fs nor the two
snaps can be trusted ? I would argue that making your fs's as small as
possible, to confine the damage, and keeping good backups is the best
option. Why would tape backup be "totally impractical even for sizes
much smaller than 4TB." ?

Who said don't make backups ? ZFS is not a backup solution but a
filesystem with checksumming and redundancy features. I've never heard
anyone seriously suggest that ZFS obviated the need for backups, not in
this thread or anywhere else. Rant about non-issues elsewhere please.

As already pointed out, increasing the number of filesystems does not
increase the protection because you still have all the common modes of
failure (including the software bugs that you are so apparently keen
on). How much better off are a million files on a single filesystem
against the same files on a thousand filesystems if everything else
remains equal? There is no meaningful difference at all.

Moreover backups do not address the OP's point - silent corruption. If
you aren't checking your files how can you have any confidence in your
backups? A backup is as problematic in terms of integrity as the
filesystem it is read from. Backing-up a corrupt file doesn't fix it.

You cannot avoid the need for checksumming to detect errors and
redundancy to fix them. Putting these features directly in your
filesystem is a good idea - integrity is maintained and there is fast
recovery. The fact that there will be teething problems in ZFS or an
equivalent filesystem is not a sound basis for rejecting these features.

There will still be backups in the future too.

ESB

I've cross-posted this question on several places, and practically all
answers switched immediately to backup/restore issues. It seems that
no-one puts any kind of trust in filesystems, in the sense that even


Filesystems are not the problem. Hardware is.

I've worked with many thousands of PC disks starting with the first
release of NTFS, almost 15 years ago. I have never seen NTFS
"corrupt" itself. All failures were traced to dying hardware. Sh*t
happens. I have to admit that my experience with RAID is much less.

I'd like to hear of documented cases of such NTFS problems.

In any case, you need a strategy for backup and recovery of your data.
Even if the filesystem is fine, the building can burn down.




--
a d y k e s @ p a n i x . c o m
Don't blame me. I voted for Gore. A Proud signature since 2001

In article .com,
Aknin wrote:
What's the maximum filesystem size you've used in production
environment? How did the experience come out?

In the NCAR Mass Storage Service (MSS), a tape archive that is approaching
3 PB in size, we currently have a disk cache of 48 TB on 4 FC-SATA RAIDs.
I have it configured as 24 logical units of just under 2 TB each, each as
a single Irix XFS file system. When a disk in the RAID fails, the controller
can rebuild the RAID group in about 4-6 hours. Files written to the
disk cache (between 112 KB and 1 GB in size) are usually written to tape
within 24 hours. Residency in the cache varies between 30-60 days. We've
not had any problems with XFS.

One option is to go with segmented filesystems: www.ibrix.com.

Instead of having one monolithic filesystem, break it up across
several segments. Ibrix still provides a single namespace. Back up the
segments separately, recover them separately.


On Apr 28, 2:21 am, Aknin wrote:
Following some research I've been doing on the matter across
newsgroups and mailing lists, I'd be glad if people could share
numbers about real life large filesystem and their experience with
them. I'm slowly coming to a realization that regardless of
theoretical filesystem capabilities (1TB, 32TB, 256TB or more), more
or less across the enterprise filesystem arena people are recommending
to keep practical filesystems up to 1TB in size, for manageability and
recoverability.

What's the maximum filesystem size you've used in production
environment? How did the experience come out?

Thanks,
-Yaniv

Filesystems are not the problem. Hardware is.

I've worked with many thousands of PC disks starting
with the first
release of NTFS, almost 15 years ago. I have never seen
NTFS
"corrupt" itself. All failures were traced to dying
hardware. Sh*t
happens. I have to admit that my experience with RAID is
much less.

I'd like to hear of documented cases of such NTFS
problems.

In any case, you need a strategy for backup and recovery
of your data.
Even if the filesystem is fine, the building can burn
down.

here's a well-known NTFS example:
http://support.microsoft.com/kb/229607

I also have another from personal experience. When you
get way out of the norm, you are much more likely to
encounter problems that have nothing to do with your
hardware. I had a case open with MS in which I was told
they had internal documentation suggesting limits that,
while beyond what you'd likely
ever see in 'normal' scenarious, are not out of the realm
of possibility for poorly-designed applications... of
which I inherited one.

Put 9 figures worth of dirs/files on a single NTFS volume
in a heavily write-intensive environment and tell me all
is well. It's very scary, and **** starts to break down,
write failures, etc. I know -- I've been there, and I'm
doing it now until such time things get rewritten. I've
lost it all more than once. Takes weeks to restore. Yes,
the app is broken, but it's what I'm stuck with for now.

Also, ask your vendors (any of them) for documented
studies of heavy IO in that type of environment. None of
them have any because for the most part, they do not test
to those levels. Even MS only tests to 100M dirs/files
for milestone releases (SPs) of Win2K3, and this is the
first release where they went that high.

You want to be safe, you'd better stay below 10M
dirs/files on a single volume. That's realistically the
highest you can go and count on all of your vendors
possibly having tested to (I'm talking file systems,
file-based replication software). You uncover the bugs
their normal stress-testing doesn't. Believe me, in
trying to deal with my mess, I've done a lot of talking to
vendors. Their sales reps tell you everything is 'not a
problem.' Their technical guys get really quiet when you
ask for proof or customer examples you can speak with.

In article ,
Kraft Fan! numberoneKraftfan@littlerockarkansasmassageschool .com wrote:
Filesystems are not the problem. Hardware is.

I've worked with many thousands of PC disks starting
with the first
release of NTFS, almost 15 years ago. I have never seen
NTFS
"corrupt" itself. All failures were traced to dying
hardware. Sh*t
happens. I have to admit that my experience with RAID is
much less.

I'd like to hear of documented cases of such NTFS
problems.

In any case, you need a strategy for backup and recovery
of your data.
Even if the filesystem is fine, the building can burn
down.

here's a well-known NTFS example:
http://support.microsoft.com/kb/229607

I also have another from personal experience. When you
get way out of the norm, you are much more likely to
encounter problems that have nothing to do with your
hardware. I had a case open with MS in which I was told
they had internal documentation suggesting limits that,


TNX, I knew there would be something and I figured it would
be a case of pushing some scale limit.

--
a d y k e s @ p a n i x . c o m
Don't blame me. I voted for Gore. A Proud signature since 2001

Kraft Fan! wrote:

....

here's a well-known NTFS example:
http://support.microsoft.com/kb/229607

Since that particular bug was fixed just over 8 years ago, something a
bit more recent might be a more convincing argument for not trusting a
reasonably mature file system.

- bill

Aknin proclaimed:

Following some research I've been doing on the matter across
newsgroups and mailing lists, I'd be glad if people could share
numbers about real life large filesystem and their experience with
them. I'm slowly coming to a realization that regardless of
theoretical filesystem capabilities (1TB, 32TB, 256TB or more), more
or less across the enterprise filesystem arena people are recommending
to keep practical filesystems up to 1TB in size, for manageability and
recoverability.

What's the maximum filesystem size you've used in production
environment? How did the experience come out?

I'd guess the biggest problem with very large file systems would be when
you need to run a file system check against them and dont have a few
days to run the check on 100 terabytes or so. Some scale better than
others, particularly if they are practically full. Backups and restores
can be helped by delta style technology.