# ZFS questions



## nORKy (Sep 30, 2010)

I remove the "solved" prefix, because I have some new question ;

There is no problem for zfs to work with Fiber Channel, right ?

I don't known how many disks to connect on my server yet. It's a FC SAN, so, I can connect many numbers of disks (LUN) I want... How choose ?

does v14 support to use a disk only for cache ?

Do you think it's good to patch 8.1 for zpool v15 (I think i'll need userquota) or I must wait for next 8.2 release ?

Thanks you


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## nORKy (Oct 5, 2010)

Can't someone tell me some idea about ZFS with SAN Fiber Channel ?


Thanks you


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## Terry_Kennedy (Oct 7, 2010)

nORKy said:
			
		

> Can't someone tell me some idea about ZFS with SAN Fiber Channel ?


Since nobody else has replied, I'll try to answer some of your questions. I'm just a user, but I have some large ZFS pools (16 x 2TB, for example).



			
				nORKy said:
			
		

> There is no problem for zfs to work with Fiber Channel, right ?
> 
> I don't known how many disks to connect on my server yet. It's a FC SAN, so, I can connect many numbers of disks (LUN) I want... How choose ?


ZFS should work over just about any disk protocol. I don't see why anything would be different with FC. If you're just using FC to make drives available to the FreeBSD system, one unit per drive. The normal ZFS configuration guidelines should apply (such as not building a single raidz device with "large" numbers of disks - try to use 6 or fewer disks per raidz device and then aggregate the raidz devices into one or more pools).



> does v14 support to use a disk only for cache ?


Yes, you can use dedicated disks for cache in v14.



> Do you think it's good to patch 8.1 for zpool v15 (I think i'll need userquota) or I must wait for next 8.2 release ?


I upgraded my systems to the latest 8-STABLE code base and did a
`# zfs upgrade`
to bring my pools up to v15. However, I did that before I placed the systems into production - if they were in production at the time, I might have waited for a future release. If you need a v15 feature, then you'll need to upgrade. I'm not aware of any timeframe for the 8.2 release (though to be honest I haven't looked lately).


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## nORKy (Oct 7, 2010)

Thanks you for reponses.
now Now, I need to find some information on how/when to use disks cache or separate ZIL disks[.]


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## User23 (Oct 7, 2010)

nORKy said:
			
		

> Thanks you for reponses.
> now Now, I need to find some information on how/when to use disks cache or separate ZIL disks[.]



Are you speaking about some special informations? Nearly all about this topic can be found on the internet.

To know "how" please take a look in zpool manpage.


```
log       A separate intent log device. If more than one log device  is
                 specified, then writes are load-balanced between devices. Log
                 devices can be mirrored. However, raidz and  raidz2  are  not
                 supported  for  the intent log. For more information, see the
                 "Intent Log" section.

       cache     A device used to cache storage pool data. A cache device can-
                 not  be  mirrored or part of a raidz or raidz2 configuration.
                 For more information, see the "Cache Devices" section.
```

For the ZIL log device, please make sure you are using a mirror, because if this device failed you cannot access the data on the pool, until you use a ZFS Version 19 or higher.

And "when" you should use the log and/or cache devices depends on your needs.

ZIL is/was mostly used on fileservers using NFS, because of the poor writing speed of NFS+ZFS without it.

The cache devices on the manpage:

```
Cache Devices
       Devices can be added to  a  storage  pool  as  "cache  devices."  These
       devices  provide an additional layer of caching between main memory and
       disk. For read-heavy workloads, where the  working  set  size  is  much
       larger  than  what  can  be  cached in main memory, using cache devices
       allow much more of this working set  to  be  served  from  low  latency
       media.  Using  cache devices provides the greatest performance improve-
       ment for random read-workloads of mostly static content.
```

http://blogs.sun.com/brendan/entry/test


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