Re: [zfs-discuss] Some ZFS questions
Neil Perrin wrote: Having said that I don't think we recommend messing with the transaction group commit timing. Yeah I don't think the customer means to tune it this way either, they were thinking of something like tune_t_fsflushr (is this still in use?) They want to know when the txg timing is a tunable. No takers for the other questions? The data checksum question is with regards to how to recover, customer wants to make sure it's not like you can do something with the checksum to get back the data (like a 1-bit detection + recovery but 2-bit detection but no recovery). I don't think it works this way but just have to check. And the PowerPath question is important, customer is using PP right now. CT ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Some ZFS questions
Additional comments below... Christine Tran wrote: Hi, I guess we are acquainted with the ZFS Wikipedia? http://en.wikipedia.org/wiki/ZFS Customers refer to it, I wonder where the Wiki gets its numbers. For example there's a Sun marketing slide that says unlimited snapshots contradicted by the the first bullet: 2^48 — Number of snapshots in any file system (2 × 10^14) Is this correct? I want to make a mirrored pool but after creation detach one side of the mirror and run like this indefinitely. Can I do this? I have yet to try it out, just wondering if someone knows the answer right off the bat. Why can't I have a vdev of type concat? A customer says he has hardware RAID-0 and does not want to stripe over stripe. Are there known problems with stripes on stripes, unintentional hotspots maybe? Friends don't let friends use RAID-0. Everyone I've known who insists on doing so has a sad story to tell. ZFS does not do concat, it does dynamic striping, which has the benefits of RAID-0 with the ability to easily expand like concat. Data checksum is used only to detect bad data, and not to recover data, correct? Just verifying. Yes, checksum is part of the detection mechanism. Correction is done by several other mechanisms, primarily using redundancy or parity reconstruction. -- richard Can I use ZFS specifically with PowerPath? I remember George W. mentioning that PowerPath tries to do something clever and it interfered with ZFS but I can't remember the specifics. Will I be able to I tune the DMU flush rate, now set at 5 seconds? CT ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Some ZFS questions
Christine Tran wrote: And the PowerPath question is important, customer is using PP right now. I haven't heard any powerpath issues. Can you track down what it was GeorgeW mentioned? ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Some ZFS questions
Torrey McMahon wrote: I haven't heard any powerpath issues. Can you track down what it was GeorgeW mentioned? Well, the problem is I can't remember. It was during a ZFS TOI class, and perhaps it was that PP tries to be clever by grouping tsx together ... If there's been no PP issue reported, that's what I'm going to have to go on, unless I have cases to the contrary. CT ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re[2]: [zfs-discuss] Some ZFS questions
Hello Torrey, Monday, December 18, 2006, 8:38:42 PM, you wrote: TM Christine Tran wrote: And the PowerPath question is important, customer is using PP right now. TM I haven't heard any powerpath issues. Can you track down what it was TM GeorgeW mentioned? H... http://www.webservertalk.com/archive100-2006-9-1594527.html It looks like IBM's software is problematic and PP works. I'm almost sure there was some problem with PP but looks like it's working (now). -- Best regards, Robertmailto:[EMAIL PROTECTED] http://milek.blogspot.com ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Some ZFS questions
CT Will I be able to I tune the DMU flush rate, now set at 5 seconds? echo 'txg_time/D 0t1' | mdb -kw Er, that 'D' ahould be a 'W'. Having said that I don't think we recommend messing with the transaction group commit timing. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
[zfs-discuss] Some ZFS questions
Hi, I guess we are acquainted with the ZFS Wikipedia? http://en.wikipedia.org/wiki/ZFS Customers refer to it, I wonder where the Wiki gets its numbers. For example there's a Sun marketing slide that says unlimited snapshots contradicted by the the first bullet: 2^48 — Number of snapshots in any file system (2 × 10^14) Is this correct? I want to make a mirrored pool but after creation detach one side of the mirror and run like this indefinitely. Can I do this? I have yet to try it out, just wondering if someone knows the answer right off the bat. Why can't I have a vdev of type concat? A customer says he has hardware RAID-0 and does not want to stripe over stripe. Are there known problems with stripes on stripes, unintentional hotspots maybe? Data checksum is used only to detect bad data, and not to recover data, correct? Just verifying. Can I use ZFS specifically with PowerPath? I remember George W. mentioning that PowerPath tries to do something clever and it interfered with ZFS but I can't remember the specifics. Will I be able to I tune the DMU flush rate, now set at 5 seconds? CT ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Some ZFS questions
Hello Christine, Saturday, December 16, 2006, 12:17:12 AM, you wrote: CT Hi, CT I guess we are acquainted with the ZFS Wikipedia? CT http://en.wikipedia.org/wiki/ZFS CT Customers refer to it, I wonder where the Wiki gets its numbers. For CT example there's a Sun marketing slide that says unlimited snapshots CT contradicted by the the first bullet: CT 2^48 — Number of snapshots in any file system (2 × 10^14) CT Is this correct? I belive it is. However 2^48 limit per file system is for every practical purpose virtually no limit, right? So when it comes to marketing I guess they get it right. CT I want to make a mirrored pool but after creation detach one side of the CT mirror and run like this indefinitely. Can I do this? I have yet to CT try it out, just wondering if someone knows the answer right off the bat. Of course you can. However you won't be able to mount detached submirror. I guess it should be quite easy to implement if needed (yes, it's needed). CT Why can't I have a vdev of type concat? A customer says he has hardware CT RAID-0 and does not want to stripe over stripe. Are there known CT problems with stripes on stripes, unintentional hotspots maybe? Depends how those stripes on HW array are actually configured and depends on data access pattern. Once you put enough data that more LUNs are used then even with concatenation you'll get into trouble (assuming pathological situation already). But generally if config is done right stripe on stripe shouldn't be a problem at all (rather should give you more performance). By pathological situation I assume config like creating a stripe from some hypers (partitions) each on differen disk, then making another stripe from other hypers on the same disks and then striping between such LUNs on a host. CT Data checksum is used only to detect bad data, and not to recover data, CT correct? Just verifying. Depends. If you do only striping in ZFS then you're right (not counting ditto blocks for meta data - however it can be useful). Once you create redundant pool in ZFS then you're not only able to detect bad data but also to correct them on the fly. That's what ZFS does automatically for you. CT Can I use ZFS specifically with PowerPath? I remember George W. CT mentioning that PowerPath tries to do something clever and it interfered CT with ZFS but I can't remember the specifics. In theory it should work. However someone else reported a problem with such a combination and IIRC it was about not exporting all LUN details by PP rather than doing anything clever by PP itself. I hope it was fixed by EMC and if not perhaps it's a good idea to fill in BUG in EMC (maybe I should test it and do it my self - just need some time). CT Will I be able to I tune the DMU flush rate, now set at 5 seconds? echo 'txg_time/D 0t1' | mdb -kw Will change it to every 1s. -- Best regards, Robertmailto:[EMAIL PROTECTED] http://milek.blogspot.com ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
