Hi,
This might be a stupid question, but I can''t figure it out.
Let''s say I''ve chosen to live with a zpool without
redundancy,
(SAN disks, has actually raid5 in disk-cabinet)
me at mybox:~# zpool status BACKUP
pool: BACKUP
state: ONLINE
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
BACKUP ONLINE 0 0 0
c0t200400A0B829BC13d0 ONLINE 0 0 0
c0t200400A0B829BC13d1 ONLINE 0 0 0
c0t200400A0B829BC13d2 ONLINE 0 0 0
errors: No known data errors
The question:
Would it be a good idea to torn OFF the ''checksum'' property of
the ZFS
filesystems?
I know the manual says it is not recommended to turn off integrity of user-data,
but what
will happen if the algorithm actually finds one? I would not have any way to
fix that, except
delete/overrite the data. (will I be able to point out what files are involved)
Yours
Espen Martinsen
--
This message posted from opensolaris.org
I''m no expert but if I was in the same situation, I would definately
keep the integrity check on. Especially since your only running a raid5, the
sooner you know there is a problem the better. Even if zfs can not fix it for
you it can still be a useful tool. Basically a few errors may not be worth
fixing manually, but if lots of errors start happening, your better off knowing
before a full drive failure. Now in certain situations, the extra overhead may
not be worth the extra relyability. But that''s a much more complex
discussion, that would need a lot more information.
------Original Message------
From: Espen Martinsen
Sender: zfs-discuss-bounces at opensolaris.org
To: zfs Discuss
Subject: [zfs-discuss] Zpool without any redundancy
Sent: Oct 20, 2009 12:49 AM
Hi,
This might be a stupid question, but I can''t figure it out.
Let''s say I''ve chosen to live with a zpool without
redundancy,
(SAN disks, has actually raid5 in disk-cabinet)
me at mybox:~# zpool status BACKUP
pool: BACKUP
state: ONLINE
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
BACKUP ONLINE 0 0 0
c0t200400A0B829BC13d0 ONLINE 0 0 0
c0t200400A0B829BC13d1 ONLINE 0 0 0
c0t200400A0B829BC13d2 ONLINE 0 0 0
errors: No known data errors
The question:
Would it be a good idea to torn OFF the ''checksum'' property of
the ZFS
filesystems?
I know the manual says it is not recommended to turn off integrity of user-data,
but what
will happen if the algorithm actually finds one? I would not have any way to
fix that, except
delete/overrite the data. (will I be able to point out what files are involved)
Yours
Espen Martinsen
--
This message posted from opensolaris.org
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On Mon, 19 Oct 2009, Espen Martinsen wrote:> Let''s say I''ve chosen to live with a zpool without redundancy, (SAN > disks, has actually raid5 in disk-cabinet)What benefit are you hoping zfs will provide in this situation? Examine your situation carefully and determine what filesystem works best for you. There are many reasons to use ZFS, but if your configuration isn''t set up to take advantage of those reasons, then there''s a disconnect somewhere.> The question: Would it be a good idea to torn OFF the ''checksum'' > property of the ZFS filesystems?No. It is never a good idea to turn off checksumming. Why run ZFS at all, then? Without checksums, it can''t detect bad data. Without redundancy, it can''t repair bad data. At least if you have checksums on, you get to know which files are corrupt and need to be restored from backup. Given the name of your pool, though ("BACKUP"), it seems to me that you''d want this to be as safe as possible. In other words, both redundancy and checksums. If you can export non-redundant disks from your cabinet, and let ZFS manage the redundancy, that seems like it would give you the best protection.> I know the manual says it is not recommended to turn off integrity of > user-data, but what will happen if the algorithm actually finds one? I > would not have any way to fix that, except delete/overrite the data. > (will I be able to point out what files are involved)Yes, with checksumming on, zfs can tell you exactly which files are bad, even in a non-redundant pool. Regards, markm
> What benefit are you hoping zfs will provide in this > situation? Examine > your situation carefully and determine what > filesystem works best for you. > There are many reasons to use ZFS, but if your > configuration isn''t set up > to take advantage of those reasons, then there''s a > disconnect somewhere.Could you elaborate this? Do you mean to say - dont use ZFS when you have a H/W raid configuration? Or create both? -- This message posted from opensolaris.org
mmusante at east.sun.com said:> What benefit are you hoping zfs will provide in this situation? Examine > your situation carefully and determine what filesystem works best for you. > There are many reasons to use ZFS, but if your configuration isn''t set up to > take advantage of those reasons, then there''s a disconnect somewhere.How about if your config can only take advantage of _some_ of those reasons to use ZFS? There are plenty of benefits to using ZFS on a single bare hard drive, and those benefits apply to using it on an expensive SAN array. It''s up to each individual to decide if adding redundancy is worthwhile or not. I''m not saying ZFS is perfect. And, ZFS is indeed better when it can make use of redundancy. But ZFS has lost data even with such redundancy, so having it does not confer magical protection from all disasters. Anyway, here''s a note describing our experience with this situation: We''ve been using ZFS here on two hardware RAID fiberchannel arrays, with no ZFS-level redundancy, starting September-2006 -- roughly 6TB of data, checksums enabled, weekly scrubs, regular tape backups. So far there has been not one checksum error detected on these arrays. We''ve had dumb SAN connectivity losses, complete power failures on arrays, FC switches, and/or file servers, and so on, but no loss of data. Before ZFS, we used a combination of SAM-QFS and UFS filesystems on the same arrays, and ZFS has proved much easier to manage, reducing data loss due to human errors in volume and space management. The checksum feature makes filesystems without it into second-class offerings, in my opinion. Is anyone else tired of seeing the word redundancy? (:-) Regards, Marion
> Is anyone else tired of seeing the word redundancy? (:-)Only in a perfect world (tm) ;-) IMHO there is no such thing as "too much redundancy". In the real world the possibilities of redundancy are only limited by money, be it "online" redundancy (mirror/RAIDZx,) "offline" redundancy (tape backups/off site disk based backups) or "infrastructure" redundancy (MPIO,..). Regards, Matthias
On Tue, 20 Oct 2009, Matthias Appel wrote:> > IMHO there is no such thing as "too much redundancy". > In the real world the possibilities of redundancy are only limited by money,Redundancy costs in terms of both time and money. Redundant hardware which fails or feels upset requires time to administer and repair. This is why there is indeed such a thing as "too much redundancy". Bob -- Bob Friesenhahn bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
> Redundancy costs in terms of both time and money. Redundant hardware > which fails or feels upset requires time to administer and repair. > This is why there is indeed such a thing as "too much redundancy".Yes that''s true, but all I wanted to say is: "If there is infinite of money there can be infinite redundancy" All the things you mentioned can be accompished by having enough money. Home users will end up with having a mirrored vdev in a "server" with non ECC RAM (IMHO ECC is also a type of redundancy). Multi billion enterprises have redundant datacenters with multiple storage arrays (another kind of redundancy). Missing time to administer the redundancy can also be compensatet with "enough mone" (hire more people). Redundancy is no rocket sience...there is enough knowledge out there to set up another level of redundancy (I am not speaking of clustering, which can indeed be limited). There is not too-much-redundancy...only a reasonable amount for your type of business needs.
>I wrote: >> Is anyone else tired of seeing the word redundancy? (:-)matthias.appel at lanlabor.com said:> Only in a perfect world (tm) ;-) > IMHO there is no such thing as "too much redundancy". In the real world the > possibilities of redundancy are only limited by money,Sigh. I was just joking about how many times the word showed up in all of our postings. http://www.imdb.com/title/tt1436296/ Marion