Brian Wilson wrote: > ----- Original Message ----- > From: Robert Milkowski <[EMAIL PROTECTED]> > Date: Thursday, August 21, 2008 5:47 am > Subject: Re: [zfs-discuss] ZFS with Traditional SAN > To: Aaron Blew <[EMAIL PROTECTED]> > Cc: zfs-discuss@opensolaris.org > > > >> Hello Aaron, >> >> >> Wednesday, August 20, 2008, 7:11:01 PM, you wrote: >> >> >> >> >> >> >> All, >> I'm currently working out details on an upgrade from UFS/SDS on DAS to >> ZFS on a SAN fabric. I'm interested in hearing how ZFS has behaved in >> more traditional SAN environments using gear that scales vertically >> like EMC Clarion/HDS AMS/3PAR etc. Do you experience issues with >> zpool integrity because of MPxIO events? Has the zpool been reliable >> over your fabric? Has performance been where you would have expected >> it to be? >> >> >> Thanks much, >> -Aaron >> >> >> >> >> >> >> >> >> Yes it works fine. >> The only issue there is, with some disk arrays, is a cache flush issue >> - you can disable it on disk array or in zfs. >> >> Then if you want to leverage ZFS self-healing properties then make >> sure you have some kind of redundancy on zfs level regardless of your >> redundancy on the array. >> >> > > That's the one that's been an issue for me and my customers - they get billed > back for GB allocated to their servers by the back end arrays. > To be more explicit about the 'self-healing properties' - > To deal with any fs corruption situation that would traditionally require an > fsck on UFS (SAN switch crash, multipathing issues, cables going flaky or > getting pulled, server crash that corrupts fs's) ZFS needs some disk > redundancy in place so it has parity and can recover. (raidz, zfs mirror, > etc) > Which means to use ZFS a customer have to pay more to get the back end > storage redundancy they need to recover from anything that would cause an > fsck on UFS. I'm not saying it's a bad implementation or that the gains > aren't worth it, just that cost-wise, ZFS is more expensive in this > particular bill-back model. >
Your understanding of UFS fsck is incorrect. It does not repair data, only metadata. ZFS has redundant metadata by default. You can also set the data redundancy on a per-file system or per-volume basis with ZFS. For example, you might want some data to be redundant, but not the whole pool. In such cases you can set the copies=2 parameter on the file systems or volumes which are more important. This is better described in pictures: http://blogs.sun.com/relling/entry/zfs_copies_and_data_protection With ZFS you can also enable compression on a per-file system or volume basis. Depending on your data, you may use less space with a mirrored (fully redundant) ZFS pool than a UFS file system. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
