From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hubert Kario Subject: Re: btrfs RAID with enterprise SATA or SAS drives Date: Thu, 10 May 2012 21:58:37 +0200 Message-ID: <1494795.CqqnWfNEaS@bursa22> References: <4FAAE94D.4010103@pocock.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Cc: linux-btrfs@vger.kernel.org To: Daniel Pocock Return-path: In-Reply-To: <4FAAE94D.4010103@pocock.com.au> List-ID: On Wednesday 09 of May 2012 22:01:49 Daniel Pocock wrote: > There is various information about > - enterprise-class drives (either SAS or just enterprise SATA) > - the SCSI/SAS protocols themselves vs SATA > having more advanced features (e.g. for dealing with error conditions= ) > than the average block device >=20 > For example, Adaptec recommends that such drives will work better wit= h > their hardware RAID cards: >=20 > http://ask.adaptec.com/cgi-bin/adaptec_tic.cfg/php/enduser/std_adp.ph= p?p_f > aqid=3D14596 "Desktop class disk drives have an error recovery featur= e that > will result in a continuous retry of the drive (read or write) when a= n > error is encountered, such as a bad sector. In a RAID array this can > cause the RAID controller to time-out while waiting for the drive to > respond." >=20 > and this blog: > http://www.adaptec.com/blog/?p=3D901 > "major advantages to enterprise drives (TLER for one) ... opt for the > enterprise drives in a RAID environment no matter what the cost of th= e > drive over the desktop drive" >=20 > My question.. >=20 > - does btrfs RAID1 actively use the more advanced features of these > drives, e.g. to work around errors without getting stuck on a bad blo= ck? There are no (short) timeouts that I know of =20 > - if a non-RAID SAS card is used, does it matter which card is chosen= ? > Does btrfs work equally well with all of them? If you're using btrfs RAID, you need a HBA, not a RAID card. If the RAI= D=20 card can work as a HBA (usually labelled as JBOD mode) then you're good= to=20 go. =46or example, HP CCISS controllers can't work in JBOD mode. If you're using the RAID feature of the card, then you need to look at=20 general Linux support, btrfs doesn't do anything other FS don't do with= the=20 block devices. =20 > - ignoring the better MTBF and seek times of these drives, do any of = the > other features passively contribute to a better RAID experience when > using btrfs? whatever they really have high MTBF values is debatable... seek times do matter very much to btrfs, fast CPU is also a good thing = to=20 have with btrfs, especially if you want to use data compression, high n= ode=20 or leaf sizes > - for someone using SAS or enterprise SATA drives with Linux, I > understand btrfs gives the extra benefit of checksums, are there any > other specific benefits over using mdadm or dmraid? Because btrfs knows when the drive is misbeheaving (because of checksum= s)=20 and is returning bad data, it can detect problems much faster then RAID= =20 (which doesn't use the reduncancy for checking if the data it's returni= ng is=20 actually correct). Both hardware and software RAID implementations depe= nd on=20 the drives to return IO errors. In effect, the data is safer on btrfs t= han=20 regular RAID. Besides that online resize (both shrinking and extending) and (currentl= y not=20 implemented) ability to set redundancy level on a per file basis. In other words, with btrfs you can have a file with RAID6 redundancy an= d a=20 second one with RAID10 level of redundancy in single directory. Regards, --=20 Hubert Kario QBS - Quality Business Software 02-656 Warszawa, ul. Ksawer=F3w 30/85 tel. +48 (22) 646-61-51, 646-74-24 www.qbs.com.pl -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html